diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index ea75943d6f314..dcdd0910aa6af 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -1803,7 +1803,11 @@ fn add_local_native_libraries(
         codegen_results.crate_info.used_libraries.iter().filter(|l| relevant_lib(sess, l));
 
     let search_path = archive_search_paths(sess);
+    let mut last = (NativeLibKind::Unspecified, None);
     for lib in relevant_libs {
+        // Skip if this library is the same as the last.
+        last = if (lib.kind, lib.name) == last { continue } else { (lib.kind, lib.name) };
+
         let name = match lib.name {
             Some(l) => l,
             None => continue,
@@ -2127,8 +2131,12 @@ fn add_upstream_native_libraries(
         .expect("failed to find crate type in dependency format list");
 
     let crates = &codegen_results.crate_info.used_crates_static;
+    let mut last = (NativeLibKind::Unspecified, None);
     for &(cnum, _) in crates {
         for lib in codegen_results.crate_info.native_libraries[&cnum].iter() {
+            // Skip if this library is the same as the last.
+            last = if (lib.kind, lib.name) == last { continue } else { (lib.kind, lib.name) };
+
             let name = match lib.name {
                 Some(l) => l,
                 None => continue,
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 77d8ab49ff258..8ba124a1fa88c 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -432,8 +432,6 @@ impl<'a> Linker for GccLinker<'a> {
         // insert it here.
         if self.sess.target.is_like_osx {
             self.linker_arg("-dead_strip");
-        } else if self.sess.target.is_like_solaris {
-            self.linker_arg("-zignore");
 
         // If we're building a dylib, we don't use --gc-sections because LLVM
         // has already done the best it can do, and we also don't want to
@@ -655,6 +653,10 @@ impl<'a> Linker for GccLinker<'a> {
     fn add_as_needed(&mut self) {
         if self.sess.target.linker_is_gnu {
             self.linker_arg("--as-needed");
+        } else if self.sess.target.is_like_solaris {
+            // -z ignore is the Solaris equivalent to the GNU ld --as-needed option
+            self.linker_arg("-z");
+            self.linker_arg("ignore");
         }
     }
 }
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index 03c83f9c07b5d..f9140609c0f3c 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -464,31 +464,9 @@ impl<'a> StripUnconfigured<'a> {
                     return true;
                 }
             };
-            let error = |span, msg, suggestion: &str| {
-                let mut err = self.sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
-                if !suggestion.is_empty() {
-                    err.span_suggestion(
-                        span,
-                        "expected syntax is",
-                        suggestion.into(),
-                        Applicability::MaybeIncorrect,
-                    );
-                }
-                err.emit();
-                true
-            };
-            let span = meta_item.span;
-            match meta_item.meta_item_list() {
-                None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
-                Some([]) => error(span, "`cfg` predicate is not specified", ""),
-                Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
-                Some([single]) => match single.meta_item() {
-                    Some(meta_item) => {
-                        attr::cfg_matches(meta_item, &self.sess.parse_sess, self.features)
-                    }
-                    None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
-                },
-            }
+            parse_cfg(&meta_item, &self.sess).map_or(true, |meta_item| {
+                attr::cfg_matches(&meta_item, &self.sess.parse_sess, self.features)
+            })
         })
     }
 
@@ -532,6 +510,32 @@ impl<'a> StripUnconfigured<'a> {
     }
 }
 
+pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a MetaItem> {
+    let error = |span, msg, suggestion: &str| {
+        let mut err = sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
+        if !suggestion.is_empty() {
+            err.span_suggestion(
+                span,
+                "expected syntax is",
+                suggestion.into(),
+                Applicability::HasPlaceholders,
+            );
+        }
+        err.emit();
+        None
+    };
+    let span = meta_item.span;
+    match meta_item.meta_item_list() {
+        None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
+        Some([]) => error(span, "`cfg` predicate is not specified", ""),
+        Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
+        Some([single]) => match single.meta_item() {
+            Some(meta_item) => Some(meta_item),
+            None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
+        },
+    }
+}
+
 fn is_cfg(sess: &Session, attr: &Attribute) -> bool {
     sess.check_name(attr, sym::cfg)
 }
diff --git a/compiler/rustc_mir/src/transform/const_goto.rs b/compiler/rustc_mir/src/transform/const_goto.rs
index b5c8b4bebc360..ba10b54c5ae2e 100644
--- a/compiler/rustc_mir/src/transform/const_goto.rs
+++ b/compiler/rustc_mir/src/transform/const_goto.rs
@@ -47,7 +47,7 @@ impl<'tcx> MirPass<'tcx> for ConstGoto {
         // if we applied optimizations, we potentially have some cfg to cleanup to
         // make it easier for further passes
         if should_simplify {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
             simplify_locals(body, tcx);
         }
     }
diff --git a/compiler/rustc_mir/src/transform/deduplicate_blocks.rs b/compiler/rustc_mir/src/transform/deduplicate_blocks.rs
index c41e71e09a4ef..912505c65983e 100644
--- a/compiler/rustc_mir/src/transform/deduplicate_blocks.rs
+++ b/compiler/rustc_mir/src/transform/deduplicate_blocks.rs
@@ -26,7 +26,7 @@ impl<'tcx> MirPass<'tcx> for DeduplicateBlocks {
         if has_opts_to_apply {
             let mut opt_applier = OptApplier { tcx, duplicates };
             opt_applier.visit_body(body);
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
index f7ea9faec4728..ac39206623308 100644
--- a/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
+++ b/compiler/rustc_mir/src/transform/early_otherwise_branch.rs
@@ -164,7 +164,7 @@ impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
         // Since this optimization adds new basic blocks and invalidates others,
         // clean up the cfg to make it nicer for other passes
         if should_cleanup {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/generator.rs b/compiler/rustc_mir/src/transform/generator.rs
index 003003a8abbea..3560b4b1e8645 100644
--- a/compiler/rustc_mir/src/transform/generator.rs
+++ b/compiler/rustc_mir/src/transform/generator.rs
@@ -964,7 +964,7 @@ fn create_generator_drop_shim<'tcx>(
 
     // Make sure we remove dead blocks to remove
     // unrelated code from the resume part of the function
-    simplify::remove_dead_blocks(&mut body);
+    simplify::remove_dead_blocks(tcx, &mut body);
 
     dump_mir(tcx, None, "generator_drop", &0, &body, |_, _| Ok(()));
 
@@ -1137,7 +1137,7 @@ fn create_generator_resume_function<'tcx>(
 
     // Make sure we remove dead blocks to remove
     // unrelated code from the drop part of the function
-    simplify::remove_dead_blocks(body);
+    simplify::remove_dead_blocks(tcx, body);
 
     dump_mir(tcx, None, "generator_resume", &0, body, |_, _| Ok(()));
 }
diff --git a/compiler/rustc_mir/src/transform/inline.rs b/compiler/rustc_mir/src/transform/inline.rs
index b6f80763bc8c4..f1c95a84ade85 100644
--- a/compiler/rustc_mir/src/transform/inline.rs
+++ b/compiler/rustc_mir/src/transform/inline.rs
@@ -57,7 +57,7 @@ impl<'tcx> MirPass<'tcx> for Inline {
         if inline(tcx, body) {
             debug!("running simplify cfg on {:?}", body.source);
             CfgSimplifier::new(body).simplify();
-            remove_dead_blocks(body);
+            remove_dead_blocks(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/match_branches.rs b/compiler/rustc_mir/src/transform/match_branches.rs
index f7a9835353e5c..21b208a08c2dc 100644
--- a/compiler/rustc_mir/src/transform/match_branches.rs
+++ b/compiler/rustc_mir/src/transform/match_branches.rs
@@ -167,7 +167,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification {
         }
 
         if should_cleanup {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
index 4aaa0baa9f46a..cd2db18055286 100644
--- a/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
+++ b/compiler/rustc_mir/src/transform/multiple_return_terminators.rs
@@ -38,6 +38,6 @@ impl<'tcx> MirPass<'tcx> for MultipleReturnTerminators {
             }
         }
 
-        simplify::remove_dead_blocks(body)
+        simplify::remove_dead_blocks(tcx, body)
     }
 }
diff --git a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
index 5144d48750de7..02e45021a0aaf 100644
--- a/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
+++ b/compiler/rustc_mir/src/transform/remove_unneeded_drops.rs
@@ -36,7 +36,7 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops {
         // if we applied optimizations, we potentially have some cfg to cleanup to
         // make it easier for further passes
         if should_simplify {
-            simplify_cfg(body);
+            simplify_cfg(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/simplify.rs b/compiler/rustc_mir/src/transform/simplify.rs
index 65e2d096b2094..63373b0cffbb0 100644
--- a/compiler/rustc_mir/src/transform/simplify.rs
+++ b/compiler/rustc_mir/src/transform/simplify.rs
@@ -29,6 +29,7 @@
 
 use crate::transform::MirPass;
 use rustc_index::vec::{Idx, IndexVec};
+use rustc_middle::mir::coverage::*;
 use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
@@ -46,9 +47,9 @@ impl SimplifyCfg {
     }
 }
 
-pub fn simplify_cfg(body: &mut Body<'_>) {
+pub fn simplify_cfg(tcx: TyCtxt<'tcx>, body: &mut Body<'_>) {
     CfgSimplifier::new(body).simplify();
-    remove_dead_blocks(body);
+    remove_dead_blocks(tcx, body);
 
     // FIXME: Should probably be moved into some kind of pass manager
     body.basic_blocks_mut().raw.shrink_to_fit();
@@ -59,9 +60,9 @@ impl<'tcx> MirPass<'tcx> for SimplifyCfg {
         Cow::Borrowed(&self.label)
     }
 
-    fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         debug!("SimplifyCfg({:?}) - simplifying {:?}", self.label, body.source);
-        simplify_cfg(body);
+        simplify_cfg(tcx, body);
     }
 }
 
@@ -286,7 +287,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
     }
 }
 
-pub fn remove_dead_blocks(body: &mut Body<'_>) {
+pub fn remove_dead_blocks(tcx: TyCtxt<'tcx>, body: &mut Body<'_>) {
     let reachable = traversal::reachable_as_bitset(body);
     let num_blocks = body.basic_blocks().len();
     if num_blocks == reachable.count() {
@@ -306,6 +307,11 @@ pub fn remove_dead_blocks(body: &mut Body<'_>) {
         }
         used_blocks += 1;
     }
+
+    if tcx.sess.instrument_coverage() {
+        save_unreachable_coverage(basic_blocks, used_blocks);
+    }
+
     basic_blocks.raw.truncate(used_blocks);
 
     for block in basic_blocks {
@@ -315,6 +321,32 @@ pub fn remove_dead_blocks(body: &mut Body<'_>) {
     }
 }
 
+fn save_unreachable_coverage(
+    basic_blocks: &mut IndexVec<BasicBlock, BasicBlockData<'_>>,
+    first_dead_block: usize,
+) {
+    // retain coverage info for dead blocks, so coverage reports will still
+    // report `0` executions for the uncovered code regions.
+    let mut dropped_coverage = Vec::new();
+    for dead_block in first_dead_block..basic_blocks.len() {
+        for statement in basic_blocks[BasicBlock::new(dead_block)].statements.iter() {
+            if let StatementKind::Coverage(coverage) = &statement.kind {
+                if let Some(code_region) = &coverage.code_region {
+                    dropped_coverage.push((statement.source_info, code_region.clone()));
+                }
+            }
+        }
+    }
+    for (source_info, code_region) in dropped_coverage {
+        basic_blocks[START_BLOCK].statements.push(Statement {
+            source_info,
+            kind: StatementKind::Coverage(box Coverage {
+                kind: CoverageKind::Unreachable,
+                code_region: Some(code_region),
+            }),
+        })
+    }
+}
 pub struct SimplifyLocals;
 
 impl<'tcx> MirPass<'tcx> for SimplifyLocals {
diff --git a/compiler/rustc_mir/src/transform/simplify_try.rs b/compiler/rustc_mir/src/transform/simplify_try.rs
index b42543c04eb3d..c9c4492062720 100644
--- a/compiler/rustc_mir/src/transform/simplify_try.rs
+++ b/compiler/rustc_mir/src/transform/simplify_try.rs
@@ -558,7 +558,7 @@ impl<'tcx> MirPass<'tcx> for SimplifyBranchSame {
 
         if did_remove_blocks {
             // We have dead blocks now, so remove those.
-            simplify::remove_dead_blocks(body);
+            simplify::remove_dead_blocks(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_mir/src/transform/unreachable_prop.rs b/compiler/rustc_mir/src/transform/unreachable_prop.rs
index 658c6b6e9db20..e7fb6b4f6b4ad 100644
--- a/compiler/rustc_mir/src/transform/unreachable_prop.rs
+++ b/compiler/rustc_mir/src/transform/unreachable_prop.rs
@@ -60,7 +60,7 @@ impl MirPass<'_> for UnreachablePropagation {
         }
 
         if replaced {
-            simplify::remove_dead_blocks(body);
+            simplify::remove_dead_blocks(tcx, body);
         }
     }
 }
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index d32180525bf70..3b21f00a001bd 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -3,6 +3,7 @@
 // from live codes are live, and everything else is dead.
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
@@ -15,7 +16,7 @@ use rustc_middle::middle::privacy;
 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
 use rustc_session::lint;
 
-use rustc_span::symbol::{sym, Symbol};
+use rustc_span::symbol::{sym, Ident, Symbol};
 
 // Any local node that may call something in its body block should be
 // explored. For example, if it's a live Node::Item that is a
@@ -507,6 +508,13 @@ fn find_live<'tcx>(
     symbol_visitor.live_symbols
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+enum ExtraNote {
+    /// Use this to provide some examples in the diagnostic of potential other purposes for a value
+    /// or field that is dead code
+    OtherPurposeExamples,
+}
+
 struct DeadVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
     live_symbols: FxHashSet<hir::HirId>,
@@ -572,14 +580,42 @@ impl DeadVisitor<'tcx> {
         &mut self,
         id: hir::HirId,
         span: rustc_span::Span,
-        name: Symbol,
+        name: Ident,
         participle: &str,
+        extra_note: Option<ExtraNote>,
     ) {
         if !name.as_str().starts_with('_') {
             self.tcx.struct_span_lint_hir(lint::builtin::DEAD_CODE, id, span, |lint| {
                 let def_id = self.tcx.hir().local_def_id(id);
                 let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
-                lint.build(&format!("{} is never {}: `{}`", descr, participle, name)).emit()
+
+                let prefixed = vec![(name.span, format!("_{}", name))];
+
+                let mut diag =
+                    lint.build(&format!("{} is never {}: `{}`", descr, participle, name));
+
+                diag.multipart_suggestion(
+                    "if this is intentional, prefix it with an underscore",
+                    prefixed,
+                    Applicability::MachineApplicable,
+                );
+
+                let mut note = format!(
+                    "the leading underscore signals that this {} serves some other \
+                    purpose even if it isn't used in a way that we can detect.",
+                    descr,
+                );
+                if matches!(extra_note, Some(ExtraNote::OtherPurposeExamples)) {
+                    note += " (e.g. for its effect when dropped or in foreign code)";
+                }
+
+                diag.note(&note);
+
+                // Force the note we added to the front, before any other subdiagnostics
+                // added in lint.build(...)
+                diag.children.rotate_right(1);
+
+                diag.emit()
             });
         }
     }
@@ -625,7 +661,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
                 hir::ItemKind::Struct(..) => "constructed", // Issue #52325
                 _ => "used",
             };
-            self.warn_dead_code(item.hir_id(), span, item.ident.name, participle);
+            self.warn_dead_code(item.hir_id(), span, item.ident, participle, None);
         } else {
             // Only continue if we didn't warn
             intravisit::walk_item(self, item);
@@ -639,7 +675,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
         id: hir::HirId,
     ) {
         if self.should_warn_about_variant(&variant) {
-            self.warn_dead_code(variant.id, variant.span, variant.ident.name, "constructed");
+            self.warn_dead_code(variant.id, variant.span, variant.ident, "constructed", None);
         } else {
             intravisit::walk_variant(self, variant, g, id);
         }
@@ -647,14 +683,20 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
 
     fn visit_foreign_item(&mut self, fi: &'tcx hir::ForeignItem<'tcx>) {
         if self.should_warn_about_foreign_item(fi) {
-            self.warn_dead_code(fi.hir_id(), fi.span, fi.ident.name, "used");
+            self.warn_dead_code(fi.hir_id(), fi.span, fi.ident, "used", None);
         }
         intravisit::walk_foreign_item(self, fi);
     }
 
     fn visit_field_def(&mut self, field: &'tcx hir::FieldDef<'tcx>) {
         if self.should_warn_about_field(&field) {
-            self.warn_dead_code(field.hir_id, field.span, field.ident.name, "read");
+            self.warn_dead_code(
+                field.hir_id,
+                field.span,
+                field.ident,
+                "read",
+                Some(ExtraNote::OtherPurposeExamples),
+            );
         }
         intravisit::walk_field_def(self, field);
     }
@@ -666,8 +708,9 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
                     self.warn_dead_code(
                         impl_item.hir_id(),
                         impl_item.span,
-                        impl_item.ident.name,
+                        impl_item.ident,
                         "used",
+                        None,
                     );
                 }
                 self.visit_nested_body(body_id)
@@ -685,7 +728,7 @@ impl Visitor<'tcx> for DeadVisitor<'tcx> {
                     } else {
                         impl_item.ident.span
                     };
-                    self.warn_dead_code(impl_item.hir_id(), span, impl_item.ident.name, "used");
+                    self.warn_dead_code(impl_item.hir_id(), span, impl_item.ident, "used", None);
                 }
                 self.visit_nested_body(body_id)
             }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 1ddd7d694547d..08d6f4a46fefe 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -2332,17 +2332,17 @@ crate mod dep_tracking {
     }
 
     macro_rules! impl_dep_tracking_hash_via_hash {
-        ($t:ty) => {
+        ($($t:ty),+ $(,)?) => {$(
             impl DepTrackingHash for $t {
                 fn hash(&self, hasher: &mut DefaultHasher, _: ErrorOutputType) {
                     Hash::hash(self, hasher);
                 }
             }
-        };
+        )+};
     }
 
     macro_rules! impl_dep_tracking_hash_for_sortable_vec_of {
-        ($t:ty) => {
+        ($($t:ty),+ $(,)?) => {$(
             impl DepTrackingHash for Vec<$t> {
                 fn hash(&self, hasher: &mut DefaultHasher, error_format: ErrorOutputType) {
                     let mut elems: Vec<&$t> = self.iter().collect();
@@ -2354,61 +2354,65 @@ crate mod dep_tracking {
                     }
                 }
             }
-        };
-    }
+        )+};
+    }
+
+    impl_dep_tracking_hash_via_hash!(
+        bool,
+        usize,
+        u64,
+        String,
+        PathBuf,
+        lint::Level,
+        Option<bool>,
+        Option<u32>,
+        Option<usize>,
+        Option<NonZeroUsize>,
+        Option<String>,
+        Option<(String, u64)>,
+        Option<Vec<String>>,
+        Option<MergeFunctions>,
+        Option<RelocModel>,
+        Option<CodeModel>,
+        Option<TlsModel>,
+        Option<WasiExecModel>,
+        Option<PanicStrategy>,
+        Option<RelroLevel>,
+        Option<InstrumentCoverage>,
+        Option<lint::Level>,
+        Option<PathBuf>,
+        CrateType,
+        MergeFunctions,
+        PanicStrategy,
+        RelroLevel,
+        Passes,
+        OptLevel,
+        LtoCli,
+        DebugInfo,
+        UnstableFeatures,
+        OutputTypes,
+        NativeLibKind,
+        SanitizerSet,
+        CFGuard,
+        TargetTriple,
+        Edition,
+        LinkerPluginLto,
+        Option<SplitDebuginfo>,
+        SwitchWithOptPath,
+        Option<SymbolManglingVersion>,
+        Option<SourceFileHashAlgorithm>,
+        TrimmedDefPaths,
+    );
 
-    impl_dep_tracking_hash_via_hash!(bool);
-    impl_dep_tracking_hash_via_hash!(usize);
-    impl_dep_tracking_hash_via_hash!(u64);
-    impl_dep_tracking_hash_via_hash!(String);
-    impl_dep_tracking_hash_via_hash!(PathBuf);
-    impl_dep_tracking_hash_via_hash!(lint::Level);
-    impl_dep_tracking_hash_via_hash!(Option<bool>);
-    impl_dep_tracking_hash_via_hash!(Option<u32>);
-    impl_dep_tracking_hash_via_hash!(Option<usize>);
-    impl_dep_tracking_hash_via_hash!(Option<NonZeroUsize>);
-    impl_dep_tracking_hash_via_hash!(Option<String>);
-    impl_dep_tracking_hash_via_hash!(Option<(String, u64)>);
-    impl_dep_tracking_hash_via_hash!(Option<Vec<String>>);
-    impl_dep_tracking_hash_via_hash!(Option<MergeFunctions>);
-    impl_dep_tracking_hash_via_hash!(Option<RelocModel>);
-    impl_dep_tracking_hash_via_hash!(Option<CodeModel>);
-    impl_dep_tracking_hash_via_hash!(Option<TlsModel>);
-    impl_dep_tracking_hash_via_hash!(Option<WasiExecModel>);
-    impl_dep_tracking_hash_via_hash!(Option<PanicStrategy>);
-    impl_dep_tracking_hash_via_hash!(Option<RelroLevel>);
-    impl_dep_tracking_hash_via_hash!(Option<InstrumentCoverage>);
-    impl_dep_tracking_hash_via_hash!(Option<lint::Level>);
-    impl_dep_tracking_hash_via_hash!(Option<PathBuf>);
-    impl_dep_tracking_hash_via_hash!(CrateType);
-    impl_dep_tracking_hash_via_hash!(MergeFunctions);
-    impl_dep_tracking_hash_via_hash!(PanicStrategy);
-    impl_dep_tracking_hash_via_hash!(RelroLevel);
-    impl_dep_tracking_hash_via_hash!(Passes);
-    impl_dep_tracking_hash_via_hash!(OptLevel);
-    impl_dep_tracking_hash_via_hash!(LtoCli);
-    impl_dep_tracking_hash_via_hash!(DebugInfo);
-    impl_dep_tracking_hash_via_hash!(UnstableFeatures);
-    impl_dep_tracking_hash_via_hash!(OutputTypes);
-    impl_dep_tracking_hash_via_hash!(NativeLibKind);
-    impl_dep_tracking_hash_via_hash!(SanitizerSet);
-    impl_dep_tracking_hash_via_hash!(CFGuard);
-    impl_dep_tracking_hash_via_hash!(TargetTriple);
-    impl_dep_tracking_hash_via_hash!(Edition);
-    impl_dep_tracking_hash_via_hash!(LinkerPluginLto);
-    impl_dep_tracking_hash_via_hash!(Option<SplitDebuginfo>);
-    impl_dep_tracking_hash_via_hash!(SwitchWithOptPath);
-    impl_dep_tracking_hash_via_hash!(Option<SymbolManglingVersion>);
-    impl_dep_tracking_hash_via_hash!(Option<SourceFileHashAlgorithm>);
-    impl_dep_tracking_hash_via_hash!(TrimmedDefPaths);
-
-    impl_dep_tracking_hash_for_sortable_vec_of!(String);
-    impl_dep_tracking_hash_for_sortable_vec_of!(PathBuf);
-    impl_dep_tracking_hash_for_sortable_vec_of!((PathBuf, PathBuf));
-    impl_dep_tracking_hash_for_sortable_vec_of!(CrateType);
-    impl_dep_tracking_hash_for_sortable_vec_of!((String, lint::Level));
-    impl_dep_tracking_hash_for_sortable_vec_of!((String, Option<String>, NativeLibKind));
-    impl_dep_tracking_hash_for_sortable_vec_of!((String, u64));
+    impl_dep_tracking_hash_for_sortable_vec_of!(
+        String,
+        PathBuf,
+        (PathBuf, PathBuf),
+        CrateType,
+        (String, lint::Level),
+        (String, Option<String>, NativeLibKind),
+        (String, u64)
+    );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)
     where
diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 73e35f0171aa7..b2e4e7a981d20 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -579,6 +579,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
 
                 let mut restrict_type_params = false;
+                let mut unsatisfied_bounds = false;
                 if !unsatisfied_predicates.is_empty() {
                     let def_span = |def_id| {
                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
@@ -739,6 +740,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         err.note(&format!(
                             "the following trait bounds were not satisfied:\n{bound_list}"
                         ));
+                        unsatisfied_bounds = true;
                     }
                 }
 
@@ -752,6 +754,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         source,
                         out_of_scope_traits,
                         &unsatisfied_predicates,
+                        unsatisfied_bounds,
                     );
                 }
 
@@ -984,9 +987,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         source: SelfSource<'tcx>,
         valid_out_of_scope_traits: Vec<DefId>,
         unsatisfied_predicates: &[(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>)],
+        unsatisfied_bounds: bool,
     ) {
         let mut alt_rcvr_sugg = false;
-        if let SelfSource::MethodCall(rcvr) = source {
+        if let (SelfSource::MethodCall(rcvr), false) = (source, unsatisfied_bounds) {
             debug!(?span, ?item_name, ?rcvr_ty, ?rcvr);
             let skippable = [
                 self.tcx.lang_items().clone_trait(),
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 415bdde11eb88..2c324b15a1a1a 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -720,9 +720,6 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 ///
 /// ## On `packed` structs
 ///
-/// It is currently impossible to create raw pointers to unaligned fields
-/// of a packed struct.
-///
 /// Attempting to create a raw pointer to an `unaligned` struct field with
 /// an expression such as `&packed.unaligned as *const FieldType` creates an
 /// intermediate unaligned reference before converting that to a raw pointer.
@@ -731,9 +728,13 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 /// As a result, using `&packed.unaligned as *const FieldType` causes immediate
 /// *undefined behavior* in your program.
 ///
+/// Instead you must use the [`ptr::addr_of!`](addr_of) macro to
+/// create the pointer. You may use that returned pointer together with this
+/// function.
+///
 /// An example of what not to do and how this relates to `read_unaligned` is:
 ///
-/// ```no_run
+/// ```
 /// #[repr(packed, C)]
 /// struct Packed {
 ///     _padding: u8,
@@ -745,24 +746,15 @@ pub const unsafe fn read<T>(src: *const T) -> T {
 ///     unaligned: 0x01020304,
 /// };
 ///
-/// #[allow(unaligned_references)]
-/// let v = unsafe {
-///     // Here we attempt to take the address of a 32-bit integer which is not aligned.
-///     let unaligned =
-///         // A temporary unaligned reference is created here which results in
-///         // undefined behavior regardless of whether the reference is used or not.
-///         &packed.unaligned
-///         // Casting to a raw pointer doesn't help; the mistake already happened.
-///         as *const u32;
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *const _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of!(packed.unaligned);
 ///
-///     let v = std::ptr::read_unaligned(unaligned);
-///
-///     v
-/// };
+/// let v = unsafe { std::ptr::read_unaligned(unaligned) };
+/// assert_eq!(v, 0x01020304);
 /// ```
 ///
 /// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however.
-// FIXME: Update docs based on outcome of RFC #2582 and friends.
 ///
 /// # Examples
 ///
@@ -916,9 +908,6 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
 ///
 /// ## On `packed` structs
 ///
-/// It is currently impossible to create raw pointers to unaligned fields
-/// of a packed struct.
-///
 /// Attempting to create a raw pointer to an `unaligned` struct field with
 /// an expression such as `&packed.unaligned as *const FieldType` creates an
 /// intermediate unaligned reference before converting that to a raw pointer.
@@ -927,36 +916,32 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
 /// As a result, using `&packed.unaligned as *const FieldType` causes immediate
 /// *undefined behavior* in your program.
 ///
-/// An example of what not to do and how this relates to `write_unaligned` is:
+/// Instead you must use the [`ptr::addr_of_mut!`](addr_of_mut)
+/// macro to create the pointer. You may use that returned pointer together with
+/// this function.
+///
+/// An example of how to do it and how this relates to `write_unaligned` is:
 ///
-/// ```no_run
+/// ```
 /// #[repr(packed, C)]
 /// struct Packed {
 ///     _padding: u8,
 ///     unaligned: u32,
 /// }
 ///
-/// let v = 0x01020304;
 /// let mut packed: Packed = unsafe { std::mem::zeroed() };
 ///
-/// #[allow(unaligned_references)]
-/// let v = unsafe {
-///     // Here we attempt to take the address of a 32-bit integer which is not aligned.
-///     let unaligned =
-///         // A temporary unaligned reference is created here which results in
-///         // undefined behavior regardless of whether the reference is used or not.
-///         &mut packed.unaligned
-///         // Casting to a raw pointer doesn't help; the mistake already happened.
-///         as *mut u32;
+/// // Take the address of a 32-bit integer which is not aligned.
+/// // In contrast to `&packed.unaligned as *mut _`, this has no undefined behavior.
+/// let unaligned = std::ptr::addr_of_mut!(packed.unaligned);
 ///
-///     std::ptr::write_unaligned(unaligned, v);
+/// unsafe { std::ptr::write_unaligned(unaligned, 42) };
 ///
-///     v
-/// };
+/// assert_eq!({packed.unaligned}, 42); // `{...}` forces copying the field instead of creating a reference.
 /// ```
 ///
-/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however.
-// FIXME: Update docs based on outcome of RFC #2582 and friends.
+/// Accessing unaligned fields directly with e.g. `packed.unaligned` is safe however
+/// (as can be seen in the `assert_eq!` above).
 ///
 /// # Examples
 ///
diff --git a/library/core/src/time.rs b/library/core/src/time.rs
index bfea39e3211fc..489b722440362 100644
--- a/library/core/src/time.rs
+++ b/library/core/src/time.rs
@@ -518,13 +518,11 @@ impl Duration {
         if let Some(mut secs) = self.secs.checked_sub(rhs.secs) {
             let nanos = if self.nanos >= rhs.nanos {
                 self.nanos - rhs.nanos
+            } else if let Some(sub_secs) = secs.checked_sub(1) {
+                secs = sub_secs;
+                self.nanos + NANOS_PER_SEC - rhs.nanos
             } else {
-                if let Some(sub_secs) = secs.checked_sub(1) {
-                    secs = sub_secs;
-                    self.nanos + NANOS_PER_SEC - rhs.nanos
-                } else {
-                    return None;
-                }
+                return None;
             };
             debug_assert!(nanos < NANOS_PER_SEC);
             Some(Duration { secs, nanos })
diff --git a/library/std/src/primitive_docs.rs b/library/std/src/primitive_docs.rs
index cd6b0b2d7ee7a..96ab32104ea2c 100644
--- a/library/std/src/primitive_docs.rs
+++ b/library/std/src/primitive_docs.rs
@@ -445,7 +445,27 @@ mod prim_unit {}
 /// Note that here the call to [`drop`] is for clarity - it indicates
 /// that we are done with the given value and it should be destroyed.
 ///
-/// ## 3. Get it from C.
+/// ## 3. Create it using `ptr::addr_of!`
+///
+/// Instead of coercing a reference to a raw pointer, you can use the macros
+/// [`ptr::addr_of!`] (for `*const T`) and [`ptr::addr_of_mut!`] (for `*mut T`).
+/// These macros allow you to create raw pointers to fields to which you cannot
+/// create a reference (without causing undefined behaviour), such as an
+/// unaligned field. This might be necessary if packed structs or uninitialized
+/// memory is involved.
+///
+/// ```
+/// #[derive(Debug, Default, Copy, Clone)]
+/// #[repr(C, packed)]
+/// struct S {
+///     aligned: u8,
+///     unaligned: u32,
+/// }
+/// let s = S::default();
+/// let p = std::ptr::addr_of!(s.unaligned); // not allowed with coercion
+/// ```
+///
+/// ## 4. Get it from C.
 ///
 /// ```
 /// # #![feature(rustc_private)]
diff --git a/library/std/src/sys/unix/os.rs b/library/std/src/sys/unix/os.rs
index 984c08c2ad531..51c3e5d175cca 100644
--- a/library/std/src/sys/unix/os.rs
+++ b/library/std/src/sys/unix/os.rs
@@ -155,12 +155,10 @@ pub fn getcwd() -> io::Result<PathBuf> {
 pub fn chdir(p: &path::Path) -> io::Result<()> {
     let p: &OsStr = p.as_ref();
     let p = CString::new(p.as_bytes())?;
-    unsafe {
-        match libc::chdir(p.as_ptr()) == (0 as c_int) {
-            true => Ok(()),
-            false => Err(io::Error::last_os_error()),
-        }
+    if unsafe { libc::chdir(p.as_ptr()) } != 0 {
+        return Err(io::Error::last_os_error());
     }
+    Ok(())
 }
 
 pub struct SplitPaths<'a> {
diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 965d11621450b..2c02dd6802621 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1197,7 +1197,7 @@ note: if you're sure you want to do this, please open an issue as to why. In the
                 .arg(builder.ensure(tool::JsonDocCk { compiler: json_compiler, target }));
         }
 
-        if mode == "run-make" && suite.ends_with("fulldeps") {
+        if mode == "run-make" && !suite.ends_with("fulldeps") {
             let rust_demangler = builder
                 .ensure(tool::RustDemangler { compiler, target, extra_features: Vec::new() })
                 .expect("in-tree tool");
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 6ad635012b134..7d67ba17b47de 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -317,10 +317,10 @@ fn merge_attrs(
             } else {
                 Attributes::from_ast(&both, None)
             },
-            both.cfg(cx.sess().diagnostic()),
+            both.cfg(cx.sess()),
         )
     } else {
-        (old_attrs.clean(cx), old_attrs.cfg(cx.sess().diagnostic()))
+        (old_attrs.clean(cx), old_attrs.cfg(cx.sess()))
     }
 }
 
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 33df9ea3f3e0c..eac9f9d969a80 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -2009,7 +2009,7 @@ fn clean_extern_crate(
         def_id: crate_def_id,
         visibility: krate.vis.clean(cx),
         kind: box ExternCrateItem { src: orig_name },
-        cfg: attrs.cfg(cx.sess().diagnostic()),
+        cfg: attrs.cfg(cx.sess()),
     }]
 }
 
diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index a556fdba2f3f6..c6969fbd77319 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -373,7 +373,7 @@ impl Item {
             kind,
             box ast_attrs.clean(cx),
             cx,
-            ast_attrs.cfg(cx.sess().diagnostic()),
+            ast_attrs.cfg(cx.sess()),
         )
     }
 
@@ -385,7 +385,7 @@ impl Item {
         cx: &mut DocContext<'_>,
         cfg: Option<Arc<Cfg>>,
     ) -> Item {
-        debug!("name={:?}, def_id={:?}", name, def_id);
+        trace!("name={:?}, def_id={:?}", name, def_id);
 
         Item {
             def_id,
@@ -730,7 +730,7 @@ crate trait AttributesExt {
 
     fn other_attrs(&self) -> Vec<ast::Attribute>;
 
-    fn cfg(&self, diagnostic: &::rustc_errors::Handler) -> Option<Arc<Cfg>>;
+    fn cfg(&self, sess: &Session) -> Option<Arc<Cfg>>;
 }
 
 impl AttributesExt for [ast::Attribute] {
@@ -755,17 +755,28 @@ impl AttributesExt for [ast::Attribute] {
         self.iter().filter(|attr| attr.doc_str().is_none()).cloned().collect()
     }
 
-    fn cfg(&self, diagnostic: &::rustc_errors::Handler) -> Option<Arc<Cfg>> {
+    fn cfg(&self, sess: &Session) -> Option<Arc<Cfg>> {
         let mut cfg = Cfg::True;
 
         for attr in self.iter() {
+            // #[doc]
             if attr.doc_str().is_none() && attr.has_name(sym::doc) {
-                if let Some(mi) = attr.meta() {
-                    if let Some(cfg_mi) = Attributes::extract_cfg(&mi) {
-                        // Extracted #[doc(cfg(...))]
-                        match Cfg::parse(cfg_mi) {
-                            Ok(new_cfg) => cfg &= new_cfg,
-                            Err(e) => diagnostic.span_err(e.span, e.msg),
+                // #[doc(...)]
+                if let Some(list) = attr.meta().as_ref().and_then(|mi| mi.meta_item_list()) {
+                    for item in list {
+                        // #[doc(include)]
+                        if !item.has_name(sym::cfg) {
+                            continue;
+                        }
+                        // #[doc(cfg(...))]
+                        if let Some(cfg_mi) = item
+                            .meta_item()
+                            .and_then(|item| rustc_expand::config::parse_cfg(&item, sess))
+                        {
+                            match Cfg::parse(&cfg_mi) {
+                                Ok(new_cfg) => cfg &= new_cfg,
+                                Err(e) => sess.span_err(e.span, e.msg),
+                            }
                         }
                     }
                 }
@@ -932,29 +943,6 @@ impl Attributes {
         self.other_attrs.lists(name)
     }
 
-    /// Extracts the content from an attribute `#[doc(cfg(content))]`.
-    crate fn extract_cfg(mi: &ast::MetaItem) -> Option<&ast::MetaItem> {
-        use rustc_ast::NestedMetaItem::MetaItem;
-
-        if let ast::MetaItemKind::List(ref nmis) = mi.kind {
-            if nmis.len() == 1 {
-                if let MetaItem(ref cfg_mi) = nmis[0] {
-                    if cfg_mi.has_name(sym::cfg) {
-                        if let ast::MetaItemKind::List(ref cfg_nmis) = cfg_mi.kind {
-                            if cfg_nmis.len() == 1 {
-                                if let MetaItem(ref content_mi) = cfg_nmis[0] {
-                                    return Some(content_mi);
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-        }
-
-        None
-    }
-
     /// Reads a `MetaItem` from within an attribute, looks for whether it is a
     /// `#[doc(include="file")]`, and returns the filename and contents of the file as loaded from
     /// its expansion.
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index 7df8b442e5acc..20eae7cf6800f 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -16,6 +16,9 @@ use rustc_middle::ty::{self, DefIdTree, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use std::mem;
 
+#[cfg(test)]
+mod tests;
+
 crate fn krate(cx: &mut DocContext<'_>) -> Crate {
     use crate::visit_lib::LibEmbargoVisitor;
 
@@ -335,11 +338,27 @@ crate fn print_evaluated_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<String>
 
 fn format_integer_with_underscore_sep(num: &str) -> String {
     let num_chars: Vec<_> = num.chars().collect();
-    let num_start_index = if num_chars.get(0) == Some(&'-') { 1 } else { 0 };
+    let mut num_start_index = if num_chars.get(0) == Some(&'-') { 1 } else { 0 };
+    let chunk_size = match num[num_start_index..].as_bytes() {
+        [b'0', b'b' | b'x', ..] => {
+            num_start_index += 2;
+            4
+        }
+        [b'0', b'o', ..] => {
+            num_start_index += 2;
+            let remaining_chars = num_chars.len() - num_start_index;
+            if remaining_chars <= 6 {
+                // don't add underscores to Unix permissions like 0755 or 100755
+                return num.to_string();
+            }
+            3
+        }
+        _ => 3,
+    };
 
     num_chars[..num_start_index]
         .iter()
-        .chain(num_chars[num_start_index..].rchunks(3).rev().intersperse(&['_']).flatten())
+        .chain(num_chars[num_start_index..].rchunks(chunk_size).rev().intersperse(&['_']).flatten())
         .collect()
 }
 
diff --git a/src/librustdoc/clean/utils/tests.rs b/src/librustdoc/clean/utils/tests.rs
new file mode 100644
index 0000000000000..ebf4b49548394
--- /dev/null
+++ b/src/librustdoc/clean/utils/tests.rs
@@ -0,0 +1,41 @@
+use super::*;
+
+#[test]
+fn int_format_decimal() {
+    assert_eq!(format_integer_with_underscore_sep("12345678"), "12_345_678");
+    assert_eq!(format_integer_with_underscore_sep("123"), "123");
+    assert_eq!(format_integer_with_underscore_sep("123459"), "123_459");
+    assert_eq!(format_integer_with_underscore_sep("-12345678"), "-12_345_678");
+    assert_eq!(format_integer_with_underscore_sep("-123"), "-123");
+    assert_eq!(format_integer_with_underscore_sep("-123459"), "-123_459");
+}
+
+#[test]
+fn int_format_hex() {
+    assert_eq!(format_integer_with_underscore_sep("0xab3"), "0xab3");
+    assert_eq!(format_integer_with_underscore_sep("0xa2345b"), "0xa2_345b");
+    assert_eq!(format_integer_with_underscore_sep("0xa2e6345b"), "0xa2e6_345b");
+    assert_eq!(format_integer_with_underscore_sep("-0xab3"), "-0xab3");
+    assert_eq!(format_integer_with_underscore_sep("-0xa2345b"), "-0xa2_345b");
+    assert_eq!(format_integer_with_underscore_sep("-0xa2e6345b"), "-0xa2e6_345b");
+}
+
+#[test]
+fn int_format_binary() {
+    assert_eq!(format_integer_with_underscore_sep("0o12345671"), "0o12_345_671");
+    assert_eq!(format_integer_with_underscore_sep("0o123"), "0o123");
+    assert_eq!(format_integer_with_underscore_sep("0o123451"), "0o123451");
+    assert_eq!(format_integer_with_underscore_sep("-0o12345671"), "-0o12_345_671");
+    assert_eq!(format_integer_with_underscore_sep("-0o123"), "-0o123");
+    assert_eq!(format_integer_with_underscore_sep("-0o123451"), "-0o123451");
+}
+
+#[test]
+fn int_format_octal() {
+    assert_eq!(format_integer_with_underscore_sep("0b101"), "0b101");
+    assert_eq!(format_integer_with_underscore_sep("0b101101011"), "0b1_0110_1011");
+    assert_eq!(format_integer_with_underscore_sep("0b01101011"), "0b0110_1011");
+    assert_eq!(format_integer_with_underscore_sep("-0b101"), "-0b101");
+    assert_eq!(format_integer_with_underscore_sep("-0b101101011"), "-0b1_0110_1011");
+    assert_eq!(format_integer_with_underscore_sep("-0b01101011"), "-0b0110_1011");
+}
diff --git a/src/librustdoc/doctest.rs b/src/librustdoc/doctest.rs
index c0157121e1923..e563889f776e5 100644
--- a/src/librustdoc/doctest.rs
+++ b/src/librustdoc/doctest.rs
@@ -1096,7 +1096,7 @@ impl<'a, 'hir, 'tcx> HirCollector<'a, 'hir, 'tcx> {
         let ast_attrs = self.tcx.hir().attrs(hir_id);
         let mut attrs = Attributes::from_ast(ast_attrs, None);
 
-        if let Some(ref cfg) = ast_attrs.cfg(self.sess.diagnostic()) {
+        if let Some(ref cfg) = ast_attrs.cfg(self.sess) {
             if !cfg.matches(&self.sess.parse_sess, Some(&self.sess.features_untracked())) {
                 return;
             }
diff --git a/src/librustdoc/html/render/context.rs b/src/librustdoc/html/render/context.rs
index 293c0a40fa799..8d1e80a9a6781 100644
--- a/src/librustdoc/html/render/context.rs
+++ b/src/librustdoc/html/render/context.rs
@@ -154,7 +154,7 @@ impl<'tcx> Context<'tcx> {
         &self.cache
     }
 
-    fn sess(&self) -> &'tcx Session {
+    pub(super) fn sess(&self) -> &'tcx Session {
         &self.shared.tcx.sess
     }
 
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index 1bf726dd31a46..b20aaaeafab77 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -292,7 +292,7 @@ fn item_module(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item, items: &[cl
                     let import_item = clean::Item {
                         def_id: import_def_id,
                         attrs: import_attrs,
-                        cfg: ast_attrs.cfg(cx.tcx().sess.diagnostic()),
+                        cfg: ast_attrs.cfg(cx.sess()),
                         ..myitem.clone()
                     };
 
diff --git a/src/test/run-make-fulldeps/coverage/compiletest-ignore-dir b/src/test/run-make-fulldeps/coverage/compiletest-ignore-dir
deleted file mode 100644
index d1824d189e382..0000000000000
--- a/src/test/run-make-fulldeps/coverage/compiletest-ignore-dir
+++ /dev/null
@@ -1,3 +0,0 @@
-# Directory "coverage" supports the tests at prefix ../coverage-*
-
-# Use ./x.py [options] test src/test/run-make-fulldeps/coverage to run all related tests.
diff --git a/src/test/run-make-fulldeps/coverage/coverage_tools.mk b/src/test/run-make-fulldeps/coverage/coverage_tools.mk
deleted file mode 100644
index aa1dc7b91ce94..0000000000000
--- a/src/test/run-make-fulldeps/coverage/coverage_tools.mk
+++ /dev/null
@@ -1,6 +0,0 @@
-# Common Makefile include for Rust `run-make-fulldeps/coverage-* tests. Include this
-# file with the line:
-#
-# -include ../coverage/coverage_tools.mk
-
--include ../tools.mk
diff --git a/src/test/run-make-fulldeps/coverage-llvmir/Makefile b/src/test/run-make/coverage-llvmir/Makefile
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-llvmir/Makefile
rename to src/test/run-make/coverage-llvmir/Makefile
diff --git a/src/test/run-make-fulldeps/coverage-llvmir/filecheck.testprog.txt b/src/test/run-make/coverage-llvmir/filecheck.testprog.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-llvmir/filecheck.testprog.txt
rename to src/test/run-make/coverage-llvmir/filecheck.testprog.txt
diff --git a/src/test/run-make-fulldeps/coverage-llvmir/testprog.rs b/src/test/run-make/coverage-llvmir/testprog.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-llvmir/testprog.rs
rename to src/test/run-make/coverage-llvmir/testprog.rs
diff --git a/src/test/run-make-fulldeps/coverage-reports/Makefile b/src/test/run-make/coverage-reports/Makefile
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/Makefile
rename to src/test/run-make/coverage-reports/Makefile
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.abort.txt b/src/test/run-make/coverage-reports/expected_show_coverage.abort.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.abort.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.abort.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.assert.txt b/src/test/run-make/coverage-reports/expected_show_coverage.assert.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.assert.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.assert.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.async.txt b/src/test/run-make/coverage-reports/expected_show_coverage.async.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.async.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.async.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.async2.txt b/src/test/run-make/coverage-reports/expected_show_coverage.async2.txt
similarity index 99%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.async2.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.async2.txt
index 8a445433ab65f..a8c79efd72356 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.async2.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.async2.txt
@@ -12,6 +12,7 @@
    12|      1|    if b {
    13|      1|        println!("non_async_func println in block");
    14|      1|    }
+                   ^0
    15|      1|}
    16|       |
    17|       |// FIXME(#83985): The auto-generated closure in an async function is failing to include
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure.txt b/src/test/run-make/coverage-reports/expected_show_coverage.closure.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.closure.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure_macro.txt b/src/test/run-make/coverage-reports/expected_show_coverage.closure_macro.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure_macro.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.closure_macro.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure_macro_async.txt b/src/test/run-make/coverage-reports/expected_show_coverage.closure_macro_async.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.closure_macro_async.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.closure_macro_async.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.conditions.txt b/src/test/run-make/coverage-reports/expected_show_coverage.conditions.txt
similarity index 93%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.conditions.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.conditions.txt
index 656a26597759d..2d8a98a5d0c92 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.conditions.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.conditions.txt
@@ -5,6 +5,7 @@
     5|      1|    if true {
     6|      1|        countdown = 10;
     7|      1|    }
+                   ^0
     8|       |
     9|       |    const B: u32 = 100;
    10|      1|    let x = if countdown > 7 {
@@ -24,6 +25,7 @@
    24|      1|    if true {
    25|      1|        countdown = 10;
    26|      1|    }
+                   ^0
    27|       |
    28|      1|    if countdown > 7 {
    29|      1|        countdown -= 4;
@@ -42,6 +44,7 @@
    41|      1|        if true {
    42|      1|            countdown = 10;
    43|      1|        }
+                       ^0
    44|       |
    45|      1|        if countdown > 7 {
    46|      1|            countdown -= 4;
@@ -54,13 +57,14 @@
    53|       |        } else {
    54|      0|            return;
    55|       |        }
-   56|       |    } // Note: closing brace shows uncovered (vs. `0` for implicit else) because condition literal
-   57|       |      // `true` was const-evaluated. The compiler knows the `if` block will be executed.
+   56|      0|    }
+   57|       |
    58|       |
    59|      1|    let mut countdown = 0;
    60|      1|    if true {
    61|      1|        countdown = 1;
    62|      1|    }
+                   ^0
    63|       |
    64|      1|    let z = if countdown > 7 {
                       ^0
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.continue.txt b/src/test/run-make/coverage-reports/expected_show_coverage.continue.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.continue.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.continue.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.dead_code.txt b/src/test/run-make/coverage-reports/expected_show_coverage.dead_code.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.dead_code.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.dead_code.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.doctest.txt b/src/test/run-make/coverage-reports/expected_show_coverage.doctest.txt
similarity index 98%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.doctest.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.doctest.txt
index 1b6bb9ff8891d..7ae0e978808e7 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.doctest.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.doctest.txt
@@ -9,7 +9,7 @@
     8|      1|//!     assert_eq!(1, 1);
     9|       |//! } else {
    10|       |//!     // this is not!
-   11|       |//!     assert_eq!(1, 2);
+   11|      0|//!     assert_eq!(1, 2);
    12|       |//! }
    13|      1|//! ```
    14|       |//!
@@ -84,7 +84,7 @@
    74|      1|    if true {
    75|      1|        assert_eq!(1, 1);
    76|       |    } else {
-   77|       |        assert_eq!(1, 2);
+   77|      0|        assert_eq!(1, 2);
    78|       |    }
    79|      1|}
    80|       |
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.drop_trait.txt b/src/test/run-make/coverage-reports/expected_show_coverage.drop_trait.txt
similarity index 87%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.drop_trait.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.drop_trait.txt
index fab5be41901c9..fe6a9e93cbf71 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.drop_trait.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.drop_trait.txt
@@ -19,11 +19,11 @@
    19|      1|    if true {
    20|      1|        println!("Exiting with error...");
    21|      1|        return Err(1);
-   22|       |    }
-   23|       |
-   24|       |    let _ = Firework { strength: 1000 };
-   25|       |
-   26|       |    Ok(())
+   22|      0|    }
+   23|      0|
+   24|      0|    let _ = Firework { strength: 1000 };
+   25|      0|
+   26|      0|    Ok(())
    27|      1|}
    28|       |
    29|       |// Expected program output:
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.generics.txt b/src/test/run-make/coverage-reports/expected_show_coverage.generics.txt
similarity index 78%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.generics.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.generics.txt
index 7b38ffb87cba8..8e8bc0fd18943 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.generics.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.generics.txt
@@ -52,15 +52,15 @@
    30|      1|    if true {
    31|      1|        println!("Exiting with error...");
    32|      1|        return Err(1);
-   33|       |    } // The remaining lines below have no coverage because `if true` (with the constant literal
-   34|       |      // `true`) is guaranteed to execute the `then` block, which is also guaranteed to `return`.
-   35|       |      // Thankfully, in the normal case, conditions are not guaranteed ahead of time, and as shown
-   36|       |      // in other tests, the lines below would have coverage (which would show they had `0`
-   37|       |      // executions, assuming the condition still evaluated to `true`).
-   38|       |
-   39|       |    let _ = Firework { strength: 1000 };
-   40|       |
-   41|       |    Ok(())
+   33|      0|    }
+   34|      0|
+   35|      0|
+   36|      0|
+   37|      0|
+   38|      0|
+   39|      0|    let _ = Firework { strength: 1000 };
+   40|      0|
+   41|      0|    Ok(())
    42|      1|}
    43|       |
    44|       |// Expected program output:
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.if.txt b/src/test/run-make/coverage-reports/expected_show_coverage.if.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.if.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.if.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.if_else.txt b/src/test/run-make/coverage-reports/expected_show_coverage.if_else.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.if_else.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.if_else.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.inline.txt b/src/test/run-make/coverage-reports/expected_show_coverage.inline.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.inline.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.inline.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.inner_items.txt b/src/test/run-make/coverage-reports/expected_show_coverage.inner_items.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.inner_items.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.inner_items.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-83601.txt b/src/test/run-make/coverage-reports/expected_show_coverage.issue-83601.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-83601.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.issue-83601.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-84561.txt b/src/test/run-make/coverage-reports/expected_show_coverage.issue-84561.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.issue-84561.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.issue-84561.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.lazy_boolean.txt b/src/test/run-make/coverage-reports/expected_show_coverage.lazy_boolean.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.lazy_boolean.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.lazy_boolean.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.loop_break_value.txt b/src/test/run-make/coverage-reports/expected_show_coverage.loop_break_value.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.loop_break_value.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.loop_break_value.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.loops_branches.txt b/src/test/run-make/coverage-reports/expected_show_coverage.loops_branches.txt
similarity index 68%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.loops_branches.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.loops_branches.txt
index 81d5c7d90346d..5d572db7cc60d 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.loops_branches.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.loops_branches.txt
@@ -9,23 +9,23 @@
     9|      1|    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
    10|      1|        if true {
    11|      1|            if false {
-   12|       |                while true {
-   13|       |                }
+   12|      0|                while true {
+   13|      0|                }
    14|      1|            }
-   15|      1|            write!(f, "error")?;
-                                            ^0
-   16|       |        } else {
-   17|       |        }
+   15|      1|            write!(f, "cool")?;
+                                           ^0
+   16|      0|        } else {
+   17|      0|        }
    18|       |
    19|     10|        for i in 0..10 {
    20|     10|            if true {
    21|     10|                if false {
-   22|       |                    while true {}
+   22|      0|                    while true {}
    23|     10|                }
-   24|     10|                write!(f, "error")?;
-                                                ^0
-   25|       |            } else {
-   26|       |            }
+   24|     10|                write!(f, "cool")?;
+                                               ^0
+   25|      0|            } else {
+   26|      0|            }
    27|       |        }
    28|      1|        Ok(())
    29|      1|    }
@@ -36,21 +36,21 @@
    34|       |impl std::fmt::Display for DisplayTest {
    35|      1|    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
    36|      1|        if false {
-   37|       |        } else {
+   37|      0|        } else {
    38|      1|            if false {
-   39|       |                while true {}
+   39|      0|                while true {}
    40|      1|            }
-   41|      1|            write!(f, "error")?;
-                                            ^0
+   41|      1|            write!(f, "cool")?;
+                                           ^0
    42|       |        }
    43|     10|        for i in 0..10 {
    44|     10|            if false {
-   45|       |            } else {
+   45|      0|            } else {
    46|     10|                if false {
-   47|       |                    while true {}
+   47|      0|                    while true {}
    48|     10|                }
-   49|     10|                write!(f, "error")?;
-                                                ^0
+   49|     10|                write!(f, "cool")?;
+                                               ^0
    50|       |            }
    51|       |        }
    52|      1|        Ok(())
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.match_or_pattern.txt b/src/test/run-make/coverage-reports/expected_show_coverage.match_or_pattern.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.match_or_pattern.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.match_or_pattern.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.nested_loops.txt b/src/test/run-make/coverage-reports/expected_show_coverage.nested_loops.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.nested_loops.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.nested_loops.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_crate.txt b/src/test/run-make/coverage-reports/expected_show_coverage.no_cov_crate.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_crate.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.no_cov_crate.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_func.txt b/src/test/run-make/coverage-reports/expected_show_coverage.no_cov_func.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.no_cov_func.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.no_cov_func.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.overflow.txt b/src/test/run-make/coverage-reports/expected_show_coverage.overflow.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.overflow.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.overflow.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.panic_unwind.txt b/src/test/run-make/coverage-reports/expected_show_coverage.panic_unwind.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.panic_unwind.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.panic_unwind.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.partial_eq.txt b/src/test/run-make/coverage-reports/expected_show_coverage.partial_eq.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.partial_eq.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.partial_eq.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.simple_loop.txt b/src/test/run-make/coverage-reports/expected_show_coverage.simple_loop.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.simple_loop.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.simple_loop.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.simple_match.txt b/src/test/run-make/coverage-reports/expected_show_coverage.simple_match.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.simple_match.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.simple_match.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.tight_inf_loop.txt b/src/test/run-make/coverage-reports/expected_show_coverage.tight_inf_loop.txt
similarity index 75%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.tight_inf_loop.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.tight_inf_loop.txt
index 5adeef7d0850b..2d4c57f451a2d 100644
--- a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.tight_inf_loop.txt
+++ b/src/test/run-make/coverage-reports/expected_show_coverage.tight_inf_loop.txt
@@ -1,6 +1,6 @@
     1|      1|fn main() {
     2|      1|    if false {
-    3|       |        loop {}
+    3|      0|        loop {}
     4|      1|    }
     5|      1|}
 
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.try_error_result.txt b/src/test/run-make/coverage-reports/expected_show_coverage.try_error_result.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.try_error_result.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.try_error_result.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.unused.txt b/src/test/run-make/coverage-reports/expected_show_coverage.unused.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.unused.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.unused.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_crate.txt b/src/test/run-make/coverage-reports/expected_show_coverage.uses_crate.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_crate.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.uses_crate.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_inline_crate.txt b/src/test/run-make/coverage-reports/expected_show_coverage.uses_inline_crate.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.uses_inline_crate.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.uses_inline_crate.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.while.txt b/src/test/run-make/coverage-reports/expected_show_coverage.while.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.while.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.while.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.while_early_ret.txt b/src/test/run-make/coverage-reports/expected_show_coverage.while_early_ret.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.while_early_ret.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.while_early_ret.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.yield.txt b/src/test/run-make/coverage-reports/expected_show_coverage.yield.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/expected_show_coverage.yield.txt
rename to src/test/run-make/coverage-reports/expected_show_coverage.yield.txt
diff --git a/src/test/run-make-fulldeps/coverage-reports/normalize_paths.py b/src/test/run-make/coverage-reports/normalize_paths.py
similarity index 100%
rename from src/test/run-make-fulldeps/coverage-reports/normalize_paths.py
rename to src/test/run-make/coverage-reports/normalize_paths.py
diff --git a/src/test/run-make-fulldeps/coverage/WARNING_KEEP_NAMES_SHORT.txt b/src/test/run-make/coverage/WARNING_KEEP_NAMES_SHORT.txt
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/WARNING_KEEP_NAMES_SHORT.txt
rename to src/test/run-make/coverage/WARNING_KEEP_NAMES_SHORT.txt
diff --git a/src/test/run-make-fulldeps/coverage/abort.rs b/src/test/run-make/coverage/abort.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/abort.rs
rename to src/test/run-make/coverage/abort.rs
diff --git a/src/test/run-make-fulldeps/coverage/assert.rs b/src/test/run-make/coverage/assert.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/assert.rs
rename to src/test/run-make/coverage/assert.rs
diff --git a/src/test/run-make-fulldeps/coverage/async.rs b/src/test/run-make/coverage/async.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/async.rs
rename to src/test/run-make/coverage/async.rs
diff --git a/src/test/run-make-fulldeps/coverage/async2.rs b/src/test/run-make/coverage/async2.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/async2.rs
rename to src/test/run-make/coverage/async2.rs
diff --git a/src/test/run-make-fulldeps/coverage/closure.rs b/src/test/run-make/coverage/closure.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/closure.rs
rename to src/test/run-make/coverage/closure.rs
diff --git a/src/test/run-make-fulldeps/coverage/closure_macro.rs b/src/test/run-make/coverage/closure_macro.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/closure_macro.rs
rename to src/test/run-make/coverage/closure_macro.rs
diff --git a/src/test/run-make-fulldeps/coverage/closure_macro_async.rs b/src/test/run-make/coverage/closure_macro_async.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/closure_macro_async.rs
rename to src/test/run-make/coverage/closure_macro_async.rs
diff --git a/src/test/run-make/coverage/compiletest-ignore-dir b/src/test/run-make/coverage/compiletest-ignore-dir
new file mode 100644
index 0000000000000..b533b272d38cf
--- /dev/null
+++ b/src/test/run-make/coverage/compiletest-ignore-dir
@@ -0,0 +1,3 @@
+# Directory "coverage" supports the tests at prefix ../coverage-*
+
+# Use ./x.py [options] test src/test/run-make/coverage to run all related tests.
diff --git a/src/test/run-make-fulldeps/coverage/conditions.rs b/src/test/run-make/coverage/conditions.rs
similarity index 90%
rename from src/test/run-make-fulldeps/coverage/conditions.rs
rename to src/test/run-make/coverage/conditions.rs
index 8a2a0b53e5862..057599d1b471a 100644
--- a/src/test/run-make-fulldeps/coverage/conditions.rs
+++ b/src/test/run-make/coverage/conditions.rs
@@ -53,8 +53,8 @@ fn main() {
         } else {
             return;
         }
-    } // Note: closing brace shows uncovered (vs. `0` for implicit else) because condition literal
-      // `true` was const-evaluated. The compiler knows the `if` block will be executed.
+    }
+
 
     let mut countdown = 0;
     if true {
diff --git a/src/test/run-make-fulldeps/coverage/continue.rs b/src/test/run-make/coverage/continue.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/continue.rs
rename to src/test/run-make/coverage/continue.rs
diff --git a/src/test/run-make/coverage/coverage_tools.mk b/src/test/run-make/coverage/coverage_tools.mk
new file mode 100644
index 0000000000000..8fce5f1b958fc
--- /dev/null
+++ b/src/test/run-make/coverage/coverage_tools.mk
@@ -0,0 +1,6 @@
+# Common Makefile include for Rust `run-make/coverage-* tests. Include this
+# file with the line:
+#
+# -include ../coverage/coverage_tools.mk
+
+-include ../../run-make-fulldeps/tools.mk
diff --git a/src/test/run-make-fulldeps/coverage/dead_code.rs b/src/test/run-make/coverage/dead_code.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/dead_code.rs
rename to src/test/run-make/coverage/dead_code.rs
diff --git a/src/test/run-make-fulldeps/coverage/doctest.rs b/src/test/run-make/coverage/doctest.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/doctest.rs
rename to src/test/run-make/coverage/doctest.rs
diff --git a/src/test/run-make-fulldeps/coverage/drop_trait.rs b/src/test/run-make/coverage/drop_trait.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/drop_trait.rs
rename to src/test/run-make/coverage/drop_trait.rs
diff --git a/src/test/run-make-fulldeps/coverage/generics.rs b/src/test/run-make/coverage/generics.rs
similarity index 67%
rename from src/test/run-make-fulldeps/coverage/generics.rs
rename to src/test/run-make/coverage/generics.rs
index cbeda35d3b8cf..18b38868496d4 100644
--- a/src/test/run-make-fulldeps/coverage/generics.rs
+++ b/src/test/run-make/coverage/generics.rs
@@ -30,11 +30,11 @@ fn main() -> Result<(),u8> {
     if true {
         println!("Exiting with error...");
         return Err(1);
-    } // The remaining lines below have no coverage because `if true` (with the constant literal
-      // `true`) is guaranteed to execute the `then` block, which is also guaranteed to `return`.
-      // Thankfully, in the normal case, conditions are not guaranteed ahead of time, and as shown
-      // in other tests, the lines below would have coverage (which would show they had `0`
-      // executions, assuming the condition still evaluated to `true`).
+    }
+
+
+
+
 
     let _ = Firework { strength: 1000 };
 
diff --git a/src/test/run-make-fulldeps/coverage/if.rs b/src/test/run-make/coverage/if.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/if.rs
rename to src/test/run-make/coverage/if.rs
diff --git a/src/test/run-make-fulldeps/coverage/if_else.rs b/src/test/run-make/coverage/if_else.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/if_else.rs
rename to src/test/run-make/coverage/if_else.rs
diff --git a/src/test/run-make-fulldeps/coverage/inline.rs b/src/test/run-make/coverage/inline.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/inline.rs
rename to src/test/run-make/coverage/inline.rs
diff --git a/src/test/run-make-fulldeps/coverage/inner_items.rs b/src/test/run-make/coverage/inner_items.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/inner_items.rs
rename to src/test/run-make/coverage/inner_items.rs
diff --git a/src/test/run-make-fulldeps/coverage/issue-83601.rs b/src/test/run-make/coverage/issue-83601.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/issue-83601.rs
rename to src/test/run-make/coverage/issue-83601.rs
diff --git a/src/test/run-make-fulldeps/coverage/issue-84561.rs b/src/test/run-make/coverage/issue-84561.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/issue-84561.rs
rename to src/test/run-make/coverage/issue-84561.rs
diff --git a/src/test/run-make-fulldeps/coverage/lazy_boolean.rs b/src/test/run-make/coverage/lazy_boolean.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/lazy_boolean.rs
rename to src/test/run-make/coverage/lazy_boolean.rs
diff --git a/src/test/run-make-fulldeps/coverage/lib/doctest_crate.rs b/src/test/run-make/coverage/lib/doctest_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/lib/doctest_crate.rs
rename to src/test/run-make/coverage/lib/doctest_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/lib/used_crate.rs b/src/test/run-make/coverage/lib/used_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/lib/used_crate.rs
rename to src/test/run-make/coverage/lib/used_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/lib/used_inline_crate.rs b/src/test/run-make/coverage/lib/used_inline_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/lib/used_inline_crate.rs
rename to src/test/run-make/coverage/lib/used_inline_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/loop_break_value.rs b/src/test/run-make/coverage/loop_break_value.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/loop_break_value.rs
rename to src/test/run-make/coverage/loop_break_value.rs
diff --git a/src/test/run-make-fulldeps/coverage/loops_branches.rs b/src/test/run-make/coverage/loops_branches.rs
similarity index 90%
rename from src/test/run-make-fulldeps/coverage/loops_branches.rs
rename to src/test/run-make/coverage/loops_branches.rs
index 4d9bbad3367f6..7116ce47f4b9d 100644
--- a/src/test/run-make-fulldeps/coverage/loops_branches.rs
+++ b/src/test/run-make/coverage/loops_branches.rs
@@ -12,7 +12,7 @@ impl std::fmt::Debug for DebugTest {
                 while true {
                 }
             }
-            write!(f, "error")?;
+            write!(f, "cool")?;
         } else {
         }
 
@@ -21,7 +21,7 @@ impl std::fmt::Debug for DebugTest {
                 if false {
                     while true {}
                 }
-                write!(f, "error")?;
+                write!(f, "cool")?;
             } else {
             }
         }
@@ -38,7 +38,7 @@ impl std::fmt::Display for DisplayTest {
             if false {
                 while true {}
             }
-            write!(f, "error")?;
+            write!(f, "cool")?;
         }
         for i in 0..10 {
             if false {
@@ -46,7 +46,7 @@ impl std::fmt::Display for DisplayTest {
                 if false {
                     while true {}
                 }
-                write!(f, "error")?;
+                write!(f, "cool")?;
             }
         }
         Ok(())
diff --git a/src/test/run-make-fulldeps/coverage/match_or_pattern.rs b/src/test/run-make/coverage/match_or_pattern.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/match_or_pattern.rs
rename to src/test/run-make/coverage/match_or_pattern.rs
diff --git a/src/test/run-make-fulldeps/coverage/nested_loops.rs b/src/test/run-make/coverage/nested_loops.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/nested_loops.rs
rename to src/test/run-make/coverage/nested_loops.rs
diff --git a/src/test/run-make-fulldeps/coverage/no_cov_crate.rs b/src/test/run-make/coverage/no_cov_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/no_cov_crate.rs
rename to src/test/run-make/coverage/no_cov_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/no_cov_func.rs b/src/test/run-make/coverage/no_cov_func.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/no_cov_func.rs
rename to src/test/run-make/coverage/no_cov_func.rs
diff --git a/src/test/run-make-fulldeps/coverage/overflow.rs b/src/test/run-make/coverage/overflow.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/overflow.rs
rename to src/test/run-make/coverage/overflow.rs
diff --git a/src/test/run-make-fulldeps/coverage/panic_unwind.rs b/src/test/run-make/coverage/panic_unwind.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/panic_unwind.rs
rename to src/test/run-make/coverage/panic_unwind.rs
diff --git a/src/test/run-make-fulldeps/coverage/partial_eq.rs b/src/test/run-make/coverage/partial_eq.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/partial_eq.rs
rename to src/test/run-make/coverage/partial_eq.rs
diff --git a/src/test/run-make-fulldeps/coverage/simple_loop.rs b/src/test/run-make/coverage/simple_loop.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/simple_loop.rs
rename to src/test/run-make/coverage/simple_loop.rs
diff --git a/src/test/run-make-fulldeps/coverage/simple_match.rs b/src/test/run-make/coverage/simple_match.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/simple_match.rs
rename to src/test/run-make/coverage/simple_match.rs
diff --git a/src/test/run-make-fulldeps/coverage/tight_inf_loop.rs b/src/test/run-make/coverage/tight_inf_loop.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/tight_inf_loop.rs
rename to src/test/run-make/coverage/tight_inf_loop.rs
diff --git a/src/test/run-make-fulldeps/coverage/try_error_result.rs b/src/test/run-make/coverage/try_error_result.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/try_error_result.rs
rename to src/test/run-make/coverage/try_error_result.rs
diff --git a/src/test/run-make-fulldeps/coverage/unused.rs b/src/test/run-make/coverage/unused.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/unused.rs
rename to src/test/run-make/coverage/unused.rs
diff --git a/src/test/run-make-fulldeps/coverage/uses_crate.rs b/src/test/run-make/coverage/uses_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/uses_crate.rs
rename to src/test/run-make/coverage/uses_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/uses_inline_crate.rs b/src/test/run-make/coverage/uses_inline_crate.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/uses_inline_crate.rs
rename to src/test/run-make/coverage/uses_inline_crate.rs
diff --git a/src/test/run-make-fulldeps/coverage/while.rs b/src/test/run-make/coverage/while.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/while.rs
rename to src/test/run-make/coverage/while.rs
diff --git a/src/test/run-make-fulldeps/coverage/while_early_ret.rs b/src/test/run-make/coverage/while_early_ret.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/while_early_ret.rs
rename to src/test/run-make/coverage/while_early_ret.rs
diff --git a/src/test/run-make-fulldeps/coverage/yield.rs b/src/test/run-make/coverage/yield.rs
similarity index 100%
rename from src/test/run-make-fulldeps/coverage/yield.rs
rename to src/test/run-make/coverage/yield.rs
diff --git a/src/test/rustdoc-ui/invalid-cfg.rs b/src/test/rustdoc-ui/invalid-cfg.rs
new file mode 100644
index 0000000000000..d237b8605c068
--- /dev/null
+++ b/src/test/rustdoc-ui/invalid-cfg.rs
@@ -0,0 +1,4 @@
+#![feature(doc_cfg)]
+#[doc(cfg = "x")] //~ ERROR not followed by parentheses
+#[doc(cfg(x, y))] //~ ERROR multiple `cfg` predicates
+struct S {}
diff --git a/src/test/rustdoc-ui/invalid-cfg.stderr b/src/test/rustdoc-ui/invalid-cfg.stderr
new file mode 100644
index 0000000000000..dae238b052b8a
--- /dev/null
+++ b/src/test/rustdoc-ui/invalid-cfg.stderr
@@ -0,0 +1,14 @@
+error: `cfg` is not followed by parentheses
+  --> $DIR/invalid-cfg.rs:2:7
+   |
+LL | #[doc(cfg = "x")]
+   |       ^^^^^^^^^ help: expected syntax is: `cfg(/* predicate */)`
+
+error: multiple `cfg` predicates are specified
+  --> $DIR/invalid-cfg.rs:3:14
+   |
+LL | #[doc(cfg(x, y))]
+   |              ^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/rustdoc/doc-cfg.rs b/src/test/rustdoc/doc-cfg.rs
index 89a61a289fdeb..1fc80b3e76c53 100644
--- a/src/test/rustdoc/doc-cfg.rs
+++ b/src/test/rustdoc/doc-cfg.rs
@@ -91,3 +91,11 @@ pub unsafe fn uses_target_feature() {
 pub fn uses_cfg_target_feature() {
     uses_target_feature();
 }
+
+// multiple attributes should be allowed
+// @has doc_cfg/fn.multiple_attrs.html \
+//  '//*[@id="main"]/*[@class="item-info"]/*[@class="stab portability"]' \
+//  'This is supported on x and y and z only.'
+#[doc(inline, cfg(x))]
+#[doc(cfg(y), cfg(z))]
+pub fn multiple_attrs() {}
diff --git a/src/test/ui/associated-consts/associated-const-dead-code.stderr b/src/test/ui/associated-consts/associated-const-dead-code.stderr
index 9b6bbb68a71f7..e9915ba9e96a5 100644
--- a/src/test/ui/associated-consts/associated-const-dead-code.stderr
+++ b/src/test/ui/associated-consts/associated-const-dead-code.stderr
@@ -2,8 +2,11 @@ error: associated constant is never used: `BAR`
   --> $DIR/associated-const-dead-code.rs:6:5
    |
 LL |     const BAR: u32 = 1;
-   |     ^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^---^^^^^^^^^^
+   |           |
+   |           help: if this is intentional, prefix it with an underscore: `_BAR`
    |
+   = note: the leading underscore signals that this associated constant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/associated-const-dead-code.rs:1:9
    |
diff --git a/src/test/ui/derive-uninhabited-enum-38885.stderr b/src/test/ui/derive-uninhabited-enum-38885.stderr
index 72607629d3c10..ff8fb9953fb53 100644
--- a/src/test/ui/derive-uninhabited-enum-38885.stderr
+++ b/src/test/ui/derive-uninhabited-enum-38885.stderr
@@ -2,8 +2,11 @@ warning: variant is never constructed: `Void`
   --> $DIR/derive-uninhabited-enum-38885.rs:13:5
    |
 LL |     Void(Void),
-   |     ^^^^^^^^^^
+   |     ----^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_Void`
    |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
    = note: `-W dead-code` implied by `-W unused`
 
 warning: 1 warning emitted
diff --git a/src/test/ui/issues/issue-37515.stderr b/src/test/ui/issues/issue-37515.stderr
index 204a39bc8e8e9..3223554a5b778 100644
--- a/src/test/ui/issues/issue-37515.stderr
+++ b/src/test/ui/issues/issue-37515.stderr
@@ -2,8 +2,11 @@ warning: type alias is never used: `Z`
   --> $DIR/issue-37515.rs:5:1
    |
 LL | type Z = dyn for<'x> Send;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^-^^^^^^^^^^^^^^^^^^^^
+   |      |
+   |      help: if this is intentional, prefix it with an underscore: `_Z`
    |
+   = note: the leading underscore signals that this type alias serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/issue-37515.rs:3:9
    |
diff --git a/src/test/ui/lint/dead-code/basic.stderr b/src/test/ui/lint/dead-code/basic.stderr
index f7b9b9c613ae0..8264d0736e03e 100644
--- a/src/test/ui/lint/dead-code/basic.stderr
+++ b/src/test/ui/lint/dead-code/basic.stderr
@@ -2,8 +2,9 @@ error: function is never used: `foo`
   --> $DIR/basic.rs:4:4
    |
 LL | fn foo() {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_foo`
    |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/basic.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/const-and-self.stderr b/src/test/ui/lint/dead-code/const-and-self.stderr
index c0e406189e8ab..e7233f386cc68 100644
--- a/src/test/ui/lint/dead-code/const-and-self.stderr
+++ b/src/test/ui/lint/dead-code/const-and-self.stderr
@@ -2,8 +2,9 @@ warning: variant is never constructed: `B`
   --> $DIR/const-and-self.rs:33:5
    |
 LL |     B,
-   |     ^
+   |     ^ help: if this is intentional, prefix it with an underscore: `_B`
    |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/const-and-self.rs:3:9
    |
@@ -14,7 +15,9 @@ warning: variant is never constructed: `C`
   --> $DIR/const-and-self.rs:34:5
    |
 LL |     C,
-   |     ^
+   |     ^ help: if this is intentional, prefix it with an underscore: `_C`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 warning: 2 warnings emitted
 
diff --git a/src/test/ui/lint/dead-code/drop-only-field-issue-81658.rs b/src/test/ui/lint/dead-code/drop-only-field-issue-81658.rs
new file mode 100644
index 0000000000000..d28b6430bc587
--- /dev/null
+++ b/src/test/ui/lint/dead-code/drop-only-field-issue-81658.rs
@@ -0,0 +1,42 @@
+//! The field `guard` is never used directly, but it is still useful for its side effect when
+//! dropped. Since rustc doesn't consider a `Drop` impl as a use, we want to make sure we at least
+//! produce a helpful diagnostic that points the user to what they can do if they indeed intended to
+//! have a field that is only used for its `Drop` side effect.
+//!
+//! Issue: https://github.com/rust-lang/rust/issues/81658
+
+#![deny(dead_code)]
+
+use std::sync::{Mutex, MutexGuard};
+
+/// Holds a locked value until it is dropped
+pub struct Locked<'a, T> {
+    // Field is kept for its affect when dropped, but otherwise unused
+    guard: MutexGuard<'a, T>, //~ ERROR field is never read
+}
+
+impl<'a, T> Locked<'a, T> {
+    pub fn new(value: &'a Mutex<T>) -> Self {
+        Self {
+            guard: value.lock().unwrap(),
+        }
+    }
+}
+
+fn main() {
+    let items = Mutex::new(vec![1, 2, 3]);
+
+    // Hold a lock on items while doing something else
+    let result = {
+        // The lock will be released at the end of this scope
+        let _lock = Locked::new(&items);
+
+        do_something_else()
+    };
+
+    println!("{}", result);
+}
+
+fn do_something_else() -> i32 {
+    1 + 1
+}
diff --git a/src/test/ui/lint/dead-code/drop-only-field-issue-81658.stderr b/src/test/ui/lint/dead-code/drop-only-field-issue-81658.stderr
new file mode 100644
index 0000000000000..f379a0941166f
--- /dev/null
+++ b/src/test/ui/lint/dead-code/drop-only-field-issue-81658.stderr
@@ -0,0 +1,17 @@
+error: field is never read: `guard`
+  --> $DIR/drop-only-field-issue-81658.rs:15:5
+   |
+LL |     guard: MutexGuard<'a, T>,
+   |     -----^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_guard`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
+note: the lint level is defined here
+  --> $DIR/drop-only-field-issue-81658.rs:8:9
+   |
+LL | #![deny(dead_code)]
+   |         ^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/lint/dead-code/empty-unused-enum.stderr b/src/test/ui/lint/dead-code/empty-unused-enum.stderr
index ed9a7ccd14b21..5c06cd5a6a0b2 100644
--- a/src/test/ui/lint/dead-code/empty-unused-enum.stderr
+++ b/src/test/ui/lint/dead-code/empty-unused-enum.stderr
@@ -2,8 +2,9 @@ error: enum is never used: `E`
   --> $DIR/empty-unused-enum.rs:3:6
    |
 LL | enum E {}
-   |      ^
+   |      ^ help: if this is intentional, prefix it with an underscore: `_E`
    |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/empty-unused-enum.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.rs b/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.rs
new file mode 100644
index 0000000000000..12eafe6ae4958
--- /dev/null
+++ b/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.rs
@@ -0,0 +1,50 @@
+//! The field `items` is being "used" by FFI (implicitly through pointers). However, since rustc
+//! doesn't know how to detect that, we produce a message that says the field is unused. This can
+//! cause some confusion and we want to make sure our diagnostics help as much as they can.
+//!
+//! Issue: https://github.com/rust-lang/rust/issues/81658
+
+#![deny(dead_code)]
+
+/// A struct for holding on to data while it is being used in our FFI code
+pub struct FFIData<T> {
+    /// These values cannot be dropped while the pointers to each item
+    /// are still in use
+    items: Option<Vec<T>>, //~ ERROR field is never read
+}
+
+impl<T> FFIData<T> {
+    pub fn new() -> Self {
+        Self {items: None}
+    }
+
+    /// Load items into this type and return pointers to each item that can
+    /// be passed to FFI
+    pub fn load(&mut self, items: Vec<T>) -> Vec<*const T> {
+        let ptrs = items.iter().map(|item| item as *const _).collect();
+
+        self.items = Some(items);
+
+        ptrs
+    }
+}
+
+extern {
+    /// The FFI code that uses items
+    fn process_item(item: *const i32);
+}
+
+fn main() {
+    // Data cannot be dropped until the end of this scope or else the items
+    // will be dropped before they are processed
+    let mut data = FFIData::new();
+
+    let ptrs = data.load(vec![1, 2, 3, 4, 5]);
+
+    for ptr in ptrs {
+        // Safety: This pointer is valid as long as the arena is in scope
+        unsafe { process_item(ptr); }
+    }
+
+    // Items will be safely freed at the end of this scope
+}
diff --git a/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.stderr b/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.stderr
new file mode 100644
index 0000000000000..d6a247d98e292
--- /dev/null
+++ b/src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.stderr
@@ -0,0 +1,17 @@
+error: field is never read: `items`
+  --> $DIR/field-used-in-ffi-issue-81658.rs:13:5
+   |
+LL |     items: Option<Vec<T>>,
+   |     -----^^^^^^^^^^^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_items`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
+note: the lint level is defined here
+  --> $DIR/field-used-in-ffi-issue-81658.rs:7:9
+   |
+LL | #![deny(dead_code)]
+   |         ^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/lint/dead-code/impl-trait.stderr b/src/test/ui/lint/dead-code/impl-trait.stderr
index 09b6d08eb8fb8..fb18eb2819f76 100644
--- a/src/test/ui/lint/dead-code/impl-trait.stderr
+++ b/src/test/ui/lint/dead-code/impl-trait.stderr
@@ -2,8 +2,11 @@ error: type alias is never used: `Unused`
   --> $DIR/impl-trait.rs:12:1
    |
 LL | type Unused = ();
-   | ^^^^^^^^^^^^^^^^^
+   | ^^^^^------^^^^^^
+   |      |
+   |      help: if this is intentional, prefix it with an underscore: `_Unused`
    |
+   = note: the leading underscore signals that this type alias serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/impl-trait.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-1.stderr b/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
index af97ea98b2b6d..15448448e1169 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-1.stderr
@@ -2,8 +2,9 @@ error: struct is never constructed: `Bar`
   --> $DIR/lint-dead-code-1.rs:12:16
    |
 LL |     pub struct Bar;
-   |                ^^^
+   |                ^^^ help: if this is intentional, prefix it with an underscore: `_Bar`
    |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/lint-dead-code-1.rs:5:9
    |
@@ -14,55 +15,77 @@ error: static is never used: `priv_static`
   --> $DIR/lint-dead-code-1.rs:20:1
    |
 LL | static priv_static: isize = 0;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^-----------^^^^^^^^^^^^
+   |        |
+   |        help: if this is intentional, prefix it with an underscore: `_priv_static`
+   |
+   = note: the leading underscore signals that this static serves some other purpose even if it isn't used in a way that we can detect.
 
 error: constant is never used: `priv_const`
   --> $DIR/lint-dead-code-1.rs:27:1
    |
 LL | const priv_const: isize = 0;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^----------^^^^^^^^^^^^
+   |       |
+   |       help: if this is intentional, prefix it with an underscore: `_priv_const`
+   |
+   = note: the leading underscore signals that this constant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: struct is never constructed: `PrivStruct`
   --> $DIR/lint-dead-code-1.rs:35:8
    |
 LL | struct PrivStruct;
-   |        ^^^^^^^^^^
+   |        ^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_PrivStruct`
+   |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 
 error: enum is never used: `priv_enum`
   --> $DIR/lint-dead-code-1.rs:64:6
    |
 LL | enum priv_enum { foo2, bar2 }
-   |      ^^^^^^^^^
+   |      ^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_priv_enum`
+   |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 
 error: variant is never constructed: `bar3`
   --> $DIR/lint-dead-code-1.rs:67:5
    |
 LL |     bar3
-   |     ^^^^
+   |     ^^^^ help: if this is intentional, prefix it with an underscore: `_bar3`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `priv_fn`
   --> $DIR/lint-dead-code-1.rs:88:4
    |
 LL | fn priv_fn() {
-   |    ^^^^^^^
+   |    ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_priv_fn`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `foo`
   --> $DIR/lint-dead-code-1.rs:93:4
    |
 LL | fn foo() {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_foo`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `bar`
   --> $DIR/lint-dead-code-1.rs:98:4
    |
 LL | fn bar() {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_bar`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `baz`
   --> $DIR/lint-dead-code-1.rs:102:4
    |
 LL | fn baz() -> impl Copy {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_baz`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 10 previous errors
 
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-2.stderr b/src/test/ui/lint/dead-code/lint-dead-code-2.stderr
index b01ba57f98580..5e19c7d02ffd3 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-2.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-2.stderr
@@ -2,8 +2,9 @@ error: function is never used: `dead_fn`
   --> $DIR/lint-dead-code-2.rs:22:4
    |
 LL | fn dead_fn() {}
-   |    ^^^^^^^
+   |    ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_dead_fn`
    |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/lint-dead-code-2.rs:2:9
    |
@@ -14,13 +15,17 @@ error: function is never used: `dead_fn2`
   --> $DIR/lint-dead-code-2.rs:25:4
    |
 LL | fn dead_fn2() {}
-   |    ^^^^^^^^
+   |    ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_dead_fn2`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `main`
   --> $DIR/lint-dead-code-2.rs:38:4
    |
 LL | fn main() {
-   |    ^^^^
+   |    ^^^^ help: if this is intentional, prefix it with an underscore: `_main`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-3.stderr b/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
index cf8f01ea19f0c..d32fde5872d99 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-3.stderr
@@ -2,8 +2,9 @@ error: struct is never constructed: `Foo`
   --> $DIR/lint-dead-code-3.rs:14:8
    |
 LL | struct Foo;
-   |        ^^^
+   |        ^^^ help: if this is intentional, prefix it with an underscore: `_Foo`
    |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/lint-dead-code-3.rs:4:9
    |
@@ -14,25 +15,35 @@ error: associated function is never used: `foo`
   --> $DIR/lint-dead-code-3.rs:16:8
    |
 LL |     fn foo(&self) {
-   |        ^^^
+   |        ^^^ help: if this is intentional, prefix it with an underscore: `_foo`
+   |
+   = note: the leading underscore signals that this associated function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `bar`
   --> $DIR/lint-dead-code-3.rs:21:4
    |
 LL | fn bar() {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_bar`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: enum is never used: `c_void`
   --> $DIR/lint-dead-code-3.rs:60:6
    |
 LL | enum c_void {}
-   |      ^^^^^^
+   |      ^^^^^^ help: if this is intentional, prefix it with an underscore: `_c_void`
+   |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `free`
   --> $DIR/lint-dead-code-3.rs:62:5
    |
 LL |     fn free(p: *const c_void);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     ^^^----^^^^^^^^^^^^^^^^^^^
+   |        |
+   |        help: if this is intentional, prefix it with an underscore: `_free`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-4.stderr b/src/test/ui/lint/dead-code/lint-dead-code-4.stderr
index 3905d1a06bdfe..2785faa29f5d9 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-4.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-4.stderr
@@ -2,8 +2,11 @@ error: field is never read: `b`
   --> $DIR/lint-dead-code-4.rs:7:5
    |
 LL |     b: bool,
-   |     ^^^^^^^
+   |     -^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_b`
    |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 note: the lint level is defined here
   --> $DIR/lint-dead-code-4.rs:3:9
    |
@@ -14,59 +17,88 @@ error: variant is never constructed: `X`
   --> $DIR/lint-dead-code-4.rs:15:5
    |
 LL |     X,
-   |     ^
+   |     ^ help: if this is intentional, prefix it with an underscore: `_X`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: variant is never constructed: `Y`
   --> $DIR/lint-dead-code-4.rs:16:5
    |
-LL | /     Y {
+LL |       Y {
+   |       ^ help: if this is intentional, prefix it with an underscore: `_Y`
+   |  _____|
+   | |
 LL | |         a: String,
 LL | |         b: i32,
 LL | |         c: i32,
 LL | |     },
    | |_____^
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: enum is never used: `ABC`
   --> $DIR/lint-dead-code-4.rs:24:6
    |
 LL | enum ABC {
-   |      ^^^
+   |      ^^^ help: if this is intentional, prefix it with an underscore: `_ABC`
+   |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 
 error: variant is never constructed: `I`
   --> $DIR/lint-dead-code-4.rs:36:5
    |
 LL |     I,
-   |     ^
+   |     ^ help: if this is intentional, prefix it with an underscore: `_I`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: field is never read: `b`
   --> $DIR/lint-dead-code-4.rs:39:9
    |
 LL |         b: i32,
-   |         ^^^^^^
+   |         -^^^^^
+   |         |
+   |         help: if this is intentional, prefix it with an underscore: `_b`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `c`
   --> $DIR/lint-dead-code-4.rs:40:9
    |
 LL |         c: i32,
-   |         ^^^^^^
+   |         -^^^^^
+   |         |
+   |         help: if this is intentional, prefix it with an underscore: `_c`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: variant is never constructed: `K`
   --> $DIR/lint-dead-code-4.rs:42:5
    |
 LL |     K
-   |     ^
+   |     ^ help: if this is intentional, prefix it with an underscore: `_K`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: field is never read: `x`
   --> $DIR/lint-dead-code-4.rs:61:5
    |
 LL |     x: usize,
-   |     ^^^^^^^^
+   |     -^^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_x`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `c`
   --> $DIR/lint-dead-code-4.rs:63:5
    |
 LL |     c: bool,
-   |     ^^^^^^^
+   |     -^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_c`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: aborting due to 10 previous errors
 
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-5.stderr b/src/test/ui/lint/dead-code/lint-dead-code-5.stderr
index 519add826273f..6375d98d35cb2 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-5.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-5.stderr
@@ -2,8 +2,9 @@ error: variant is never constructed: `Variant2`
   --> $DIR/lint-dead-code-5.rs:6:5
    |
 LL |     Variant2
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_Variant2`
    |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/lint-dead-code-5.rs:2:9
    |
@@ -14,19 +15,29 @@ error: variant is never constructed: `Variant5`
   --> $DIR/lint-dead-code-5.rs:13:5
    |
 LL |     Variant5 { _x: isize },
-   |     ^^^^^^^^^^^^^^^^^^^^^^
+   |     --------^^^^^^^^^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_Variant5`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: variant is never constructed: `Variant6`
   --> $DIR/lint-dead-code-5.rs:14:5
    |
 LL |     Variant6(isize),
-   |     ^^^^^^^^^^^^^^^
+   |     --------^^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_Variant6`
+   |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 
 error: enum is never used: `Enum3`
   --> $DIR/lint-dead-code-5.rs:35:6
    |
 LL | enum Enum3 {
-   |      ^^^^^
+   |      ^^^^^ help: if this is intentional, prefix it with an underscore: `_Enum3`
+   |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/lint/dead-code/lint-dead-code-6.stderr b/src/test/ui/lint/dead-code/lint-dead-code-6.stderr
index 7dc60730d6aad..ef26fe54ab589 100644
--- a/src/test/ui/lint/dead-code/lint-dead-code-6.stderr
+++ b/src/test/ui/lint/dead-code/lint-dead-code-6.stderr
@@ -2,8 +2,9 @@ error: struct is never constructed: `UnusedStruct`
   --> $DIR/lint-dead-code-6.rs:3:8
    |
 LL | struct UnusedStruct;
-   |        ^^^^^^^^^^^^
+   |        ^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_UnusedStruct`
    |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/lint-dead-code-6.rs:1:9
    |
@@ -14,19 +15,25 @@ error: associated function is never used: `unused_impl_fn_1`
   --> $DIR/lint-dead-code-6.rs:5:8
    |
 LL |     fn unused_impl_fn_1() {
-   |        ^^^^^^^^^^^^^^^^
+   |        ^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused_impl_fn_1`
+   |
+   = note: the leading underscore signals that this associated function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: associated function is never used: `unused_impl_fn_2`
   --> $DIR/lint-dead-code-6.rs:9:8
    |
 LL |     fn unused_impl_fn_2(var: i32) {
-   |        ^^^^^^^^^^^^^^^^
+   |        ^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused_impl_fn_2`
+   |
+   = note: the leading underscore signals that this associated function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: associated function is never used: `unused_impl_fn_3`
   --> $DIR/lint-dead-code-6.rs:13:8
    |
 LL |     fn unused_impl_fn_3(
-   |        ^^^^^^^^^^^^^^^^
+   |        ^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused_impl_fn_3`
+   |
+   = note: the leading underscore signals that this associated function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/lint/dead-code/newline-span.stderr b/src/test/ui/lint/dead-code/newline-span.stderr
index fd74405f2b648..5bd566be35e01 100644
--- a/src/test/ui/lint/dead-code/newline-span.stderr
+++ b/src/test/ui/lint/dead-code/newline-span.stderr
@@ -2,8 +2,9 @@ error: function is never used: `unused`
   --> $DIR/newline-span.rs:3:4
    |
 LL | fn unused() {
-   |    ^^^^^^
+   |    ^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused`
    |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/newline-span.rs:1:9
    |
@@ -14,13 +15,17 @@ error: function is never used: `unused2`
   --> $DIR/newline-span.rs:7:4
    |
 LL | fn unused2(var: i32) {
-   |    ^^^^^^^
+   |    ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused2`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: function is never used: `unused3`
   --> $DIR/newline-span.rs:11:4
    |
 LL | fn unused3(
-   |    ^^^^^^^
+   |    ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_unused3`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/lint/dead-code/type-alias.stderr b/src/test/ui/lint/dead-code/type-alias.stderr
index b2acd5d4213b3..1e7a030de3aa7 100644
--- a/src/test/ui/lint/dead-code/type-alias.stderr
+++ b/src/test/ui/lint/dead-code/type-alias.stderr
@@ -2,8 +2,11 @@ error: type alias is never used: `Unused`
   --> $DIR/type-alias.rs:4:1
    |
 LL | type Unused = u8;
-   | ^^^^^^^^^^^^^^^^^
+   | ^^^^^------^^^^^^
+   |      |
+   |      help: if this is intentional, prefix it with an underscore: `_Unused`
    |
+   = note: the leading underscore signals that this type alias serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/type-alias.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/unused-enum.stderr b/src/test/ui/lint/dead-code/unused-enum.stderr
index 9f368fdd2f816..d536479c800ae 100644
--- a/src/test/ui/lint/dead-code/unused-enum.stderr
+++ b/src/test/ui/lint/dead-code/unused-enum.stderr
@@ -2,8 +2,9 @@ error: struct is never constructed: `F`
   --> $DIR/unused-enum.rs:3:8
    |
 LL | struct F;
-   |        ^
+   |        ^ help: if this is intentional, prefix it with an underscore: `_F`
    |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/unused-enum.rs:1:9
    |
@@ -15,13 +16,17 @@ error: struct is never constructed: `B`
   --> $DIR/unused-enum.rs:4:8
    |
 LL | struct B;
-   |        ^
+   |        ^ help: if this is intentional, prefix it with an underscore: `_B`
+   |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 
 error: enum is never used: `E`
   --> $DIR/unused-enum.rs:6:6
    |
 LL | enum E {
-   |      ^
+   |      ^ help: if this is intentional, prefix it with an underscore: `_E`
+   |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/lint/dead-code/unused-struct-variant.stderr b/src/test/ui/lint/dead-code/unused-struct-variant.stderr
index b93d6d4ac1866..394ced3e81001 100644
--- a/src/test/ui/lint/dead-code/unused-struct-variant.stderr
+++ b/src/test/ui/lint/dead-code/unused-struct-variant.stderr
@@ -2,8 +2,11 @@ error: variant is never constructed: `Bar`
   --> $DIR/unused-struct-variant.rs:8:5
    |
 LL |     Bar(B),
-   |     ^^^^^^
+   |     ---^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_Bar`
    |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/unused-struct-variant.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/unused-variant.stderr b/src/test/ui/lint/dead-code/unused-variant.stderr
index a547f5af4b082..7dcb79d0490c1 100644
--- a/src/test/ui/lint/dead-code/unused-variant.stderr
+++ b/src/test/ui/lint/dead-code/unused-variant.stderr
@@ -2,8 +2,9 @@ error: variant is never constructed: `Variant1`
   --> $DIR/unused-variant.rs:5:5
    |
 LL |     Variant1,
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_Variant1`
    |
+   = note: the leading underscore signals that this variant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/unused-variant.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/with-core-crate.stderr b/src/test/ui/lint/dead-code/with-core-crate.stderr
index 2c63e60d67609..1bde434069ee7 100644
--- a/src/test/ui/lint/dead-code/with-core-crate.stderr
+++ b/src/test/ui/lint/dead-code/with-core-crate.stderr
@@ -2,8 +2,9 @@ error: function is never used: `foo`
   --> $DIR/with-core-crate.rs:7:4
    |
 LL | fn foo() {
-   |    ^^^
+   |    ^^^ help: if this is intentional, prefix it with an underscore: `_foo`
    |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/with-core-crate.rs:1:9
    |
diff --git a/src/test/ui/lint/dead-code/write-only-field.stderr b/src/test/ui/lint/dead-code/write-only-field.stderr
index a191d22c8b94c..13a21bb1193de 100644
--- a/src/test/ui/lint/dead-code/write-only-field.stderr
+++ b/src/test/ui/lint/dead-code/write-only-field.stderr
@@ -2,8 +2,11 @@ error: field is never read: `f`
   --> $DIR/write-only-field.rs:4:5
    |
 LL |     f: i32,
-   |     ^^^^^^
+   |     -^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_f`
    |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 note: the lint level is defined here
   --> $DIR/write-only-field.rs:1:9
    |
@@ -14,31 +17,51 @@ error: field is never read: `sub`
   --> $DIR/write-only-field.rs:5:5
    |
 LL |     sub: Sub,
-   |     ^^^^^^^^
+   |     ---^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_sub`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `f`
   --> $DIR/write-only-field.rs:9:5
    |
 LL |     f: i32,
-   |     ^^^^^^
+   |     -^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_f`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `y`
   --> $DIR/write-only-field.rs:28:9
    |
 LL |         y: bool,
-   |         ^^^^^^^
+   |         -^^^^^^
+   |         |
+   |         help: if this is intentional, prefix it with an underscore: `_y`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `u`
   --> $DIR/write-only-field.rs:58:9
    |
 LL |         u: u32,
-   |         ^^^^^^
+   |         -^^^^^
+   |         |
+   |         help: if this is intentional, prefix it with an underscore: `_u`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `v`
   --> $DIR/write-only-field.rs:59:9
    |
 LL |         v: u32,
-   |         ^^^^^^
+   |         -^^^^^
+   |         |
+   |         help: if this is intentional, prefix it with an underscore: `_v`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/lint/issue-17718-const-naming.stderr b/src/test/ui/lint/issue-17718-const-naming.stderr
index ce4ebcb5e3ef6..e880006e114c1 100644
--- a/src/test/ui/lint/issue-17718-const-naming.stderr
+++ b/src/test/ui/lint/issue-17718-const-naming.stderr
@@ -2,8 +2,11 @@ error: constant is never used: `foo`
   --> $DIR/issue-17718-const-naming.rs:4:1
    |
 LL | const foo: isize = 3;
-   | ^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^---^^^^^^^^^^^^
+   |       |
+   |       help: if this is intentional, prefix it with an underscore: `_foo`
    |
+   = note: the leading underscore signals that this constant serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/issue-17718-const-naming.rs:2:9
    |
diff --git a/src/test/ui/span/macro-span-replacement.stderr b/src/test/ui/span/macro-span-replacement.stderr
index 45cf5f8688cd1..f94a9e30a3dfa 100644
--- a/src/test/ui/span/macro-span-replacement.stderr
+++ b/src/test/ui/span/macro-span-replacement.stderr
@@ -2,11 +2,14 @@ warning: struct is never constructed: `S`
   --> $DIR/macro-span-replacement.rs:7:14
    |
 LL |         $b $a;
-   |              ^
+   |            --^
+   |            |
+   |            help: if this is intentional, prefix it with an underscore: `_S`
 ...
 LL |     m!(S struct);
    |     ------------- in this macro invocation
    |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/macro-span-replacement.rs:3:9
    |
diff --git a/src/test/ui/span/unused-warning-point-at-identifier.stderr b/src/test/ui/span/unused-warning-point-at-identifier.stderr
index 6ef877da122f5..3bf342f197252 100644
--- a/src/test/ui/span/unused-warning-point-at-identifier.stderr
+++ b/src/test/ui/span/unused-warning-point-at-identifier.stderr
@@ -2,8 +2,9 @@ warning: enum is never used: `Enum`
   --> $DIR/unused-warning-point-at-identifier.rs:5:6
    |
 LL | enum Enum {
-   |      ^^^^
+   |      ^^^^ help: if this is intentional, prefix it with an underscore: `_Enum`
    |
+   = note: the leading underscore signals that this enum serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/unused-warning-point-at-identifier.rs:3:9
    |
@@ -15,19 +16,25 @@ warning: struct is never constructed: `Struct`
   --> $DIR/unused-warning-point-at-identifier.rs:12:8
    |
 LL | struct Struct {
-   |        ^^^^^^
+   |        ^^^^^^ help: if this is intentional, prefix it with an underscore: `_Struct`
+   |
+   = note: the leading underscore signals that this struct serves some other purpose even if it isn't used in a way that we can detect.
 
 warning: function is never used: `func`
   --> $DIR/unused-warning-point-at-identifier.rs:19:4
    |
 LL | fn func() -> usize {
-   |    ^^^^
+   |    ^^^^ help: if this is intentional, prefix it with an underscore: `_func`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 warning: function is never used: `func_complete_span`
   --> $DIR/unused-warning-point-at-identifier.rs:24:1
    |
 LL | func_complete_span()
-   | ^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_func_complete_span`
+   |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 
 warning: 4 warnings emitted
 
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.rs b/src/test/ui/suggestions/import-trait-for-method-call.rs
index 646f68dea14e8..4dbadbdf98206 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.rs
+++ b/src/test/ui/suggestions/import-trait-for-method-call.rs
@@ -6,4 +6,11 @@ fn next_u64() -> u64 {
     h.finish() //~ ERROR no method named `finish` found for struct `DefaultHasher`
 }
 
-fn main() {}
+trait Bar {}
+impl Bar for String {}
+
+fn main() {
+    let s = String::from("hey");
+    let x: &dyn Bar = &s;
+    x.as_ref(); //~ ERROR the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds
+}
diff --git a/src/test/ui/suggestions/import-trait-for-method-call.stderr b/src/test/ui/suggestions/import-trait-for-method-call.stderr
index f3ae20552f3d5..a2b9b9d14ab09 100644
--- a/src/test/ui/suggestions/import-trait-for-method-call.stderr
+++ b/src/test/ui/suggestions/import-trait-for-method-call.stderr
@@ -15,6 +15,22 @@ help: the following trait is implemented but not in scope; perhaps add a `use` f
 LL | use std::hash::Hasher;
    |
 
-error: aborting due to previous error
+error[E0599]: the method `as_ref` exists for reference `&dyn Bar`, but its trait bounds were not satisfied
+  --> $DIR/import-trait-for-method-call.rs:15:7
+   |
+LL | trait Bar {}
+   | --------- doesn't satisfy `dyn Bar: AsRef<_>`
+...
+LL |     x.as_ref();
+   |       ^^^^^^ method cannot be called on `&dyn Bar` due to unsatisfied trait bounds
+   |
+   = note: the following trait bounds were not satisfied:
+           `dyn Bar: AsRef<_>`
+           which is required by `&dyn Bar: AsRef<_>`
+   = help: items from traits can only be used if the trait is implemented and in scope
+   = note: the following trait defines an item `as_ref`, perhaps you need to implement it:
+           candidate #1: `AsRef`
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0599`.
diff --git a/src/test/ui/test-attrs/test-warns-dead-code.stderr b/src/test/ui/test-attrs/test-warns-dead-code.stderr
index d3bcea2951364..e5a8dee6ccb68 100644
--- a/src/test/ui/test-attrs/test-warns-dead-code.stderr
+++ b/src/test/ui/test-attrs/test-warns-dead-code.stderr
@@ -2,8 +2,9 @@ error: function is never used: `dead`
   --> $DIR/test-warns-dead-code.rs:5:4
    |
 LL | fn dead() {}
-   |    ^^^^
+   |    ^^^^ help: if this is intentional, prefix it with an underscore: `_dead`
    |
+   = note: the leading underscore signals that this function serves some other purpose even if it isn't used in a way that we can detect.
 note: the lint level is defined here
   --> $DIR/test-warns-dead-code.rs:3:9
    |
diff --git a/src/test/ui/union/union-fields-1.stderr b/src/test/ui/union/union-fields-1.stderr
index 87621cc01b1b9..3595bf6dce688 100644
--- a/src/test/ui/union/union-fields-1.stderr
+++ b/src/test/ui/union/union-fields-1.stderr
@@ -2,8 +2,11 @@ error: field is never read: `c`
   --> $DIR/union-fields-1.rs:6:5
    |
 LL |     c: u8,
-   |     ^^^^^
+   |     -^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_c`
    |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 note: the lint level is defined here
   --> $DIR/union-fields-1.rs:1:9
    |
@@ -14,19 +17,31 @@ error: field is never read: `a`
   --> $DIR/union-fields-1.rs:9:5
    |
 LL |     a: u8,
-   |     ^^^^^
+   |     -^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_a`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `a`
   --> $DIR/union-fields-1.rs:13:20
    |
 LL | union NoDropLike { a: u8 }
-   |                    ^^^^^
+   |                    -^^^^
+   |                    |
+   |                    help: if this is intentional, prefix it with an underscore: `_a`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: field is never read: `c`
   --> $DIR/union-fields-1.rs:18:5
    |
 LL |     c: u8,
-   |     ^^^^^
+   |     -^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_c`
+   |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/union/union-lint-dead-code.stderr b/src/test/ui/union/union-lint-dead-code.stderr
index 7de70ec33801f..8ead9cde9b333 100644
--- a/src/test/ui/union/union-lint-dead-code.stderr
+++ b/src/test/ui/union/union-lint-dead-code.stderr
@@ -2,8 +2,11 @@ error: field is never read: `b`
   --> $DIR/union-lint-dead-code.rs:5:5
    |
 LL |     b: bool,
-   |     ^^^^^^^
+   |     -^^^^^^
+   |     |
+   |     help: if this is intentional, prefix it with an underscore: `_b`
    |
+   = note: the leading underscore signals that this field serves some other purpose even if it isn't used in a way that we can detect. (e.g. for its effect when dropped or in foreign code)
 note: the lint level is defined here
   --> $DIR/union-lint-dead-code.rs:1:9
    |